Alan Mannus

3.1. Linfield F.C.

Mannus began his football journey at Linfield at the age of sixteen, progressing through the club's junior ranks. He was loaned out to Larne, making one appearance in a 1-1 draw against Ards on 22 October 2000. He then had a loan spell at Carrick Rangers, where he made nine appearances.

In the 2001-02 season, Mannus was an unused substitute in the first qualifying round of the UEFA Champions League against Torpedo Kutaisi, a tie Linfield lost 1-0 on aggregate. He made his senior debut for Linfield on 24 October 2001, in a 3-0 win against Bangor. Following this, he established himself as the club's first-choice goalkeeper. He helped Linfield secure a spot in the UEFA Cup by defeating Omagh Town 3-2 on 28 April 2002. Mannus also played a crucial role in the club's Irish Cup victory, a 2-1 win over Portadown. He described this period as a "fairy tale," having gone from uncertainty about his future a year prior to winning the Irish Cup. Days later, he helped Linfield Swifts win the Belfast Telegraph Intermediate Cup, securing a double for himself that season. He later credited the arrival of Tommy Wright as goalkeeper coach for transforming his career.

Mannus succeeded Robert Robinson as Linfield's primary goalkeeper at the start of the 2002-03 season. He played in both legs of the UEFA Cup qualification round against Stabæk, which Linfield lost 5-1 on aggregate. On 25 September 2002, he saved a penalty from Michael O'Neill in a 1-1 draw against Glentoran. He suffered a thigh injury on 23 October 2002, against Glenavon, but returned to the starting lineup on 8 December 2002, in a 2-0 win against Crusaders. He then kept five consecutive clean sheets in the league between 8 February and 22 March 2003, and three more between 12 April and 22 April 2003. Despite his strong performances, the club finished fourth in the league and failed to win any trophies that season.

In the 2003-04 season, Mannus contributed to Linfield's six-match unbeaten run in the group stage of the Irish League Cup. He also kept five consecutive clean sheets between 11 October and 1 November 2003. Notably, in a match against Omagh Town in 2003, Mannus became one of the rare goalkeepers to score a goal from open play, as his long goal kick bounced over the opposing goalkeeper and into the net. This achievement earned him the Player of the Month award for October 2003. His performances were crucial to the team's title challenge. In a 3-1 win against Glentoran on 28 December 2003, he was fortunate not to be sent off after a confrontation with opposing player Andy Smith. By February, he had kept eleven clean sheets in twenty matches. Mannus started in the County Antrim Shield final, a 2-0 win against Ards, securing the trophy. He then recorded six consecutive clean sheets in the league between 28 February and 18 April 2004, helping Linfield win the league championship with a 2-1 victory over Glentoran on 25 April 2004. He was named to the Belfast Telegraph Team of the Season and was nominated for the Northern Ireland Football Writers' Association Player of the Year award, which he lost to teammate Glenn Ferguson. At the end of the season, Mannus signed a two-year contract extension.

The 2004-05 season saw Mannus play in both legs of the UEFA Champions League first qualifying round against HJK, which Linfield lost 2-0 on aggregate. Despite the European exit, he helped the club maintain strong league form. He played a key role in Linfield's 2-1 victory over Cliftonville in the Irish League Cup semi-finals. Although he acknowledged frustration with goals conceded, he started in the final, where Linfield lost 2-1. In January 2005, Mannus was linked with moves to Everton and Doncaster Rovers. He helped Linfield reach and win the County Antrim Shield final for the second consecutive year, beating Crusaders 2-1. On his 150th appearance for Linfield, against Glentoran on 23 April 2005, he played through injury but the club lost 3-2. Linfield ultimately failed to defend their league title. However, Mannus was in goal for the Setanta Cup final against Shelbourne, where Linfield won 2-0 to claim the inaugural tournament. For the second consecutive season, he was named to the Belfast Telegraph Team of the Season.

At the start of the 2005-06 season, Mannus's performance in a friendly against Rangers earned praise from both managers, David Jeffrey and Alex McLeish, with suggestions that he should turn professional. He played in both legs of the UEFA Cup first qualifying round against FK Ventspils, which Linfield won on away goals. However, in the second qualifying round against Halmstads BK, Linfield lost 5-3 on aggregate. Following this, Mannus set a target for the club to win four trophies that season. He helped Linfield dominate the league, leading the table, and kept three consecutive clean sheets between 22 October and 5 November 2005. On 10 December 2005, he helped the club win their first trophy of the season, the Irish League Cup, with a 3-0 victory over Glentoran. In the second half of the season, he maintained five consecutive clean sheets in the league between 2 January and 4 February 2006. He then helped Linfield secure their second trophy, the County Antrim Shield, by beating Ballymena United 2-1. By March, Mannus had made forty-seven appearances. He helped the club win their third trophy, the league title, on 18 March 2006, with a 1-0 win against Armagh City. Mannus then helped Linfield win their fourth trophy, the Irish Cup, beating Glentoran 2-1, thus fulfilling his season's target. He finished the season with fifty-seven appearances, thirty-one clean sheets, and forty-one goals conceded.

In the 2006-07 season, Mannus played in both legs of the UEFA Champions League first qualifying round against ND Gorica, which Linfield lost 5-3 on aggregate. Following their European exit, he warned other Northern Irish teams about Linfield's blistering form. The following month, Mannus signed a three-year professional deal with Linfield. He kept six consecutive clean sheets in the league between 21 October and 25 November 2006, attributing this success to the entire team's defensive effort. On 26 February 2007, he made his 250th appearance for the club in a 4-0 Setanta Sports Cup win against Drogheda United. Mannus appeared in almost every match, missing only one due to international duty. He returned for the Irish Cup quarter-final replay against Ballymena United, which Linfield won 4-2. He helped Linfield win the league for the second consecutive time on 14 April 2007, beating Glentoran 2-1. He then played a pivotal role in the Irish Cup final victory over Dungannon Swifts, saving three penalties in the shootout after a 2-2 draw. However, Linfield narrowly missed out on a treble, losing the Setanta Sports Cup final to Drogheda United on penalties, despite Mannus saving two penalties during the game and shootout.

The 2007-08 season saw Mannus play in both legs of the UEFA Champions League first qualifying round against IF Elfsborg, which Linfield lost 1-0 on aggregate. In the Irish Cup semi-final against Newry Town, he saved a penalty in the shootout, helping Linfield win 4-3 after a 1-1 draw. He then kept four consecutive clean sheets in the league between 24 November and 15 December 2007. Mannus started in the Irish League Cup final, a 3-2 win against Crusaders, securing his first trophy of the season. On the final day of the season, he helped Linfield win the league title with a 3-0 victory over Crusaders. A week later, on 3 May 2008, he started in the Irish Cup final against Coleraine, which Linfield won 2-1, marking their third trophy of the season. For his outstanding performances in April, Mannus was named the 2007-08 Ulster Footballer of the Year.

Ahead of the 2008-09 season, manager David Jeffrey confirmed Mannus would not be sold. He played in both legs of the UEFA Champions League first qualifying round against IF Elfsborg, which Linfield lost 3-1 on aggregate. Despite dental problems, Mannus started in a 1-0 win against Newry City on 23 August 2008, followed by a 7-0 clean sheet victory against Institute. After a period of poor form for Linfield in October, Mannus expressed his determination to win another trophy. However, he declined a new contract offer from Linfield, which led to interest from Scottish Premier League side Motherwell. Amid speculation about his future, Mannus kept three consecutive clean sheets in the league between 20 December 2008 and 1 January 2009, helping Linfield return to the top of the table. In February, he conceded only two goals in all competitions. On 27 April 2009, David Jeffrey expected Mannus to leave the club for England or Scotland. Mannus compared Linfield's high expectations to a "robot" due to the constant demands on players. Linfield's poor results ultimately led to them losing the league title to Glentoran on the final day.

During his time at Linfield, Mannus became a fan favourite, contributing to numerous trophy wins, including the Irish League/Irish Premier League, Irish League Cup, and County Antrim Shield. Upon the expiration of his contract, he was linked with Swansea City and reportedly trained with Falkirk. In July 2009, he had a trial with English League Two side Bradford City, playing three games without conceding, but was ultimately released.

3.2. Shamrock Rovers F.C. (First Spell)

On 4 August 2009, Mannus signed an 18-month contract with Shamrock Rovers. Initially the second-choice goalkeeper behind Barry Murphy, he made his debut for Michael O'Neill's side in a 2-2 draw against Dundalk on 22 August 2009. He quickly established himself as the club's first-choice goalkeeper and kept three consecutive clean sheets in the league between 2 October and 17 October 2009. However, Shamrock Rovers failed to secure the league title, drawing 1-1 against Galway United on 30 October 2009. He made eleven appearances in all competitions during the 2009 season.

Ahead of the 2010 season, Mannus officially became Shamrock Rovers' primary goalkeeper after Murphy's departure. After a slow start with only one point from the first three league matches, he improved his performances, and the club's results followed. He kept three consecutive clean sheets in the league between 9 April and 23 April 2010. On 15 May 2010, he helped the club beat UCD. In a match against St Patrick's Athletic on 5 July 2010, Mannus saved a last-minute penalty from Ryan Guy, securing a 2-1 win. He played in both legs of the UEFA Europa League second qualifying round against Bnei Yehuda Tel Aviv, helping the club advance with a 2-1 aggregate win. Mannus then played in both legs of the third qualifying round against Juventus, where Shamrock Rovers were eliminated after a 3-0 aggregate loss. Despite a mid-season dip in form, including a 5-1 loss to Dundalk, Mannus helped Shamrock Rovers win the League of Ireland for the first time since 1995, securing the title in the final two matches. After winning his first title with the club, Mannus stated he had no regrets about the move, even if it impacted his international career. In the FAI Cup final against Sligo Rovers, the game ended in a goalless draw after 120 minutes, but Shamrock Rovers lost 2-0 in the penalty shootout. Mannus played in every match during the 2010 season, making fifty appearances in all competitions. He was nominated for the PFAI Players' Player of the Year award, which he lost to Richie Ryan. However, he was awarded the SWAI Goalkeeper of the Year and named to the PFAI Team of the Year.

Before the 2011 season, Mannus signed a contract extension with Shamrock Rovers. He helped the club keep four consecutive clean sheets in the league between 12 March and 1 April 2011, and another three between 6 May and 20 May 2011. In the Setanta Sports Cup final against Dundalk, he helped Shamrock Rovers win 2-0 to secure the trophy. Despite a shoulder injury, Mannus started in a 4-0 FAI Cup third-round win against Athlone Town. In his final match for the club on 19 July 2011, he kept a clean sheet in a 0-0 draw away to Flora Tallinn in the Champions League second qualifying round second leg, helping the team advance 1-0 on aggregate. By the time he left, Mannus had made twenty-four appearances in all competitions for Shamrock Rovers. Even after his departure, he received a medal when Shamrock Rovers won the league for the second consecutive time.

3.3. St Johnstone F.C.

On 21 July 2011, Mannus signed a one-year contract with Scottish Premier League side St Johnstone. This move was facilitated by a clause in his Shamrock Rovers contract that allowed him to leave if a British club made an offer after 20 July 2011.

Initially, Mannus served as a backup goalkeeper to Peter Enckelman for seven months. However, after Enckelman conceded five goals against Dundee United on 11 February 2012, with two mistakes, manager Steve Lomas considered replacing him. Mannus made his debut for the Saints in the Scottish Cup fifth round replay against Hearts on 14 February 2012, a 2-1 loss. In his league debut, he kept a clean sheet in a 0-0 draw against Aberdeen. He quickly displaced Enckelman as the first-choice goalkeeper and helped the Saints improve their results towards the end of the season. Mannus believed that playing first-team football would benefit his international career. On 21 April 2012, he signed a 12-month contract extension. He helped St Johnstone qualify for European competition despite finishing sixth in the league.

At the start of the 2012-13 season, Mannus played in both legs of the UEFA Europa League second qualifying round against Turkish side Eskişehirspor, which St Johnstone lost 4-1 on aggregate. In a match against Celtic on 15 September 2012, he made several crucial saves, helping the Saints to a 2-1 victory. On 27 October 2012, against Inverness Caledonian Thistle, Mannus saved a penalty from Andrew Shinnie before assisting David Robertson's equalizing goal in a 1-1 draw. He made impressive saves against Kenny McLean and David van Zanten in a 1-1 draw against St Mirren on 8 December 2012. In a 2-0 loss against Aberdeen on 22 December 2012, his "four or five great saves" prevented a worse scoreline, though he admitted fault for one of the goals conceded. In a 1-1 draw against Celtic on 20 February 2013, he again produced strong saves from Gary Hooper and Lassad Nouioui. On the final day of the season, he helped the club win 2-0, securing a third-place finish and qualification for Europe again. Mannus made forty-one appearances in all competitions that season and signed another one-year contract. For his performances, he received the Jailers Tours Player of the Year, SJFC Supporters' Bus Player of the Year, and Barbosa Street Saints Player of the Year awards.

The 2013-14 season began well for Mannus, keeping a clean sheet in a 1-0 away win against Norwegian side Rosenborg on 18 July 2013, in the Europa League second qualifying round first leg. After a 1-1 draw in the second leg saw St Johnstone advance 2-1 on aggregate, he suggested that Rosenborg had been "arrogant" and underestimated his team. Mannus played in both legs of the UEFA Europa League third qualifying round against Minsk, keeping a clean sheet in the first leg. In the return leg, he conceded a goal, leading to extra time and a penalty shootout, where despite saving two penalties, the club was eliminated. Following this, Mannus kept two clean sheets in the first two league matches against Hearts and Kilmarnock. However, he sustained a dislocated shoulder against Kilmarnock, sidelining him for six weeks, though he returned to training earlier than expected. He made his return on 14 September 2013, in a 2-1 loss against Hibernian, with manager Tommy Wright praising his comeback. He helped St Johnstone keep three consecutive clean sheets across all competitions between 27 October and 2 November 2013. On 18 January 2014, in a 3-3 draw against Hearts, Mannus was sent off along with Ryan Stevenson after an altercation. The club decided not to appeal his red card. While serving his suspension, he fractured a bone in his thumb, which was expected to keep him out for six to eight weeks. However, he returned to the starting lineup two weeks later, on 16 February 2014, in a 3-0 loss against Celtic, playing with a metal splint and tape to support his thumb. On 21 February 2014, Mannus signed a new one-year contract, extending his stay until May 2015. In a 1-1 draw against Partick Thistle on 28 March 2014, he conceded a late goal, but manager Tommy Wright defended him, confident he would bounce back. In the Scottish Cup semi-finals against Aberdeen on 13 April 2014, Mannus helped St Johnstone win 2-1 to reach the final. In the final against Dundee United, he made several crucial saves as the Saints won 2-0, securing the first major trophy in their 130-year history. He made forty-four appearances in all competitions that season.

At the start of the 2014-15 season, Mannus played in both legs of the UEFA Europa League second qualifying round against Luzern. After a 2-2 aggregate draw, he saved a penalty in the shootout, helping St Johnstone win 5-4 to advance. However, in the third qualifying round against Spartak Trnava, the Saints were eliminated. Following a poor start to the league season, Mannus helped the team improve their results and kept three consecutive clean sheets between 6 December and 20 December 2014. He stated his goal was to achieve more clean sheets. In a 2-0 loss against Aberdeen on 1 January 2015, Mannus made several saves, including a 25-yard save from Jonny Hayes, despite conceding two goals, ending the club's eight-match unbeaten run. Manager Tommy Wright praised his "outstanding" performance. He then kept three consecutive clean sheets in the league between 21 February and 4 March 2015. With his contract expiring, St Johnstone began talks for an extension, and on 6 April 2015, he signed a new two-year deal until 2017. Mannus was an ever-present player throughout the 2014-15 season, helping St Johnstone beat Aberdeen 1-0 on the final day to qualify for the UEFA Europa League for the third consecutive year. He made forty-six appearances in all competitions and received the We Are Perth Exiles 'Player of the Year' and George Gordon 'Clubman of the Year' awards.

Ahead of the 2015-16 season, Mannus faced competition from the returning goalkeeper, Zander Clark. He started the first leg of the UEFA Europa League first qualifying round against FC Alashkert, conceding the only goal in a 1-0 loss. Despite his optimism for the return leg, St Johnstone were eliminated on away goals. In the opening league game against Hearts, he conceded a penalty but saved the initial shot before a rebound goal, as St Johnstone lost 4-3. On 26 September 2015, he received a straight red card for bringing down Billy Mckay against Dundee United, though the Saints still won 2-1. The club chose not to appeal the red card. He returned from suspension on 17 October 2015, in a 2-1 loss against Partick Thistle, stating his desire to maintain form for UEFA Euro 2016 selection. After his first clean sheet of the season against Inverness Caledonian Thistle on 24 October 2015, Mannus expressed his determination to help St Johnstone achieve more clean sheets. He captained the Saints for the first time in a 2-0 loss against Dundee on 12 February 2016. His form dipped, leading to him being at fault for four goals in losses against Dundee United and Kilmarnock. As a result, he was temporarily replaced by Zander Clark as first-choice goalkeeper. He returned for the final game of the season, a 2-2 draw against Hearts. Mannus made thirty-nine appearances in all competitions that season.

The 2016-17 season saw continued competition with Zander Clark for the starting role. Mannus started two Scottish League Cup group stage matches, helping St Johnstone advance. He also helped the Saints beat Hearts 3-2 in the last 16 of the Scottish League Cup. His performances against Celtic and Inverness Caledonian Thistle were praised despite losses. However, an illness led to him being benched, with Clark taking over for most of the season. Mannus made only one appearance for the rest of 2016, in a 4-2 loss against Ross County on 19 November 2016. He returned to the first team on 18 March 2017, as a second-half substitute for an injured Clark in a 2-1 win against Motherwell. Following this, Mannus regained his first-choice status for the remainder of the season. On 29 April 2017, he made his 200th appearance for the Saints in a 2-0 win against Aberdeen. His contributions helped the club qualify for the UEFA Europa League. He made seventeen appearances in all competitions and signed a one-year contract extension.

The 2017-18 season again featured competition between Mannus and Zander Clark. Mannus was the first-choice goalkeeper for the first ten league matches, with his performances praised. However, his form soon dipped, coinciding with poor results for St Johnstone. He was subsequently dropped in favour of Clark. Mannus returned to the starting lineup on 29 January 2018, in a 4-0 Scottish Cup fourth-round win against Albion Rovers, regaining his first-choice role for most of the second half of the season. In a match against Rangers on 27 February 2018, Mannus conceded a penalty and was booked, leading to a 4-1 loss. He criticized referee Steven McLean's decision. On 17 April 2018, St Johnstone announced that Mannus would leave the club upon his contract's expiration. After being benched in late April, he made his final appearance for the club as captain against Ross County on the last game of the season, a 1-1 draw. He made twenty-five appearances in all competitions during his last season with St Johnstone.

3.4. Shamrock Rovers F.C. (Second Spell)

On 18 April 2018, Mannus signed a pre-contract with Shamrock Rovers, marking his second spell with the club, effective from 1 July 2018.

He made his second debut for Shamrock Rovers on 22 July 2018, keeping a clean sheet in a 1-0 win against Waterford. He quickly displaced Gavin Bazunu as the first-choice goalkeeper and played every minute of their league campaign. Mannus kept five consecutive clean sheets in the league between 31 August and 12 October 2018. He made eleven appearances in all competitions during the 2018 season.

Ahead of the 2019 season, Mannus expressed his aim to win trophies, acknowledging Shamrock Rovers' high expectations. He helped the club keep five consecutive clean sheets in the league between 1 March and 22 March 2019. He fully regained his first-choice goalkeeper role following Gavin Bazunu's departure. He contributed to another three consecutive clean sheets in the league between 17 May and 24 May 2019. On 8 June 2019, Mannus made his 100th appearance for Shamrock Rovers in a 2-2 draw against Derry City. He then helped the club achieve another three consecutive clean sheets in the league between 1 July and 21 July 2019. Mannus played in both legs of the UEFA Europa League first qualifying round against SK Brann, helping Shamrock Rovers advance 4-3 on aggregate. However, in the second qualifying round against Apollon Limassol, the club was eliminated after a 4-3 aggregate loss. Mannus later helped Shamrock Rovers defeat Bohemian in the FAI Cup semi-finals to reach the final. He kept four consecutive clean sheets in the remaining four league matches, as the club finished second. Mannus started in the final against Dundalk, playing all 120 minutes of a 1-1 draw and making crucial saves in the penalty shootout to lift the FAI Cup. The Irish Independent praised his goalkeeping performance in the final. However, Mannus caused controversy by refusing to turn to face the flag of the Republic of Ireland during the national anthem. He later stated he did not intend to offend and did so because he is not Irish. He made forty-five appearances in all competitions during the 2019 season and was named to the PFAI Team of the Year.

At the start of the 2020 season, Mannus helped Shamrock Rovers keep three consecutive clean sheets in the first three league matches. During a 3-2 win against Sligo Rovers on 7 March 2020, he reported alleged sectarian abuse from opposition supporters to the referee and the Football Association of Ireland. He made five appearances before the season was suspended due to the COVID-19 pandemic. When the season resumed behind closed doors, Mannus helped the club beat Finn Harps on 1 August 2020. He again contributed to three consecutive clean sheets in the league between 16 August and 5 September 2020. Mannus made a crucial save in the club's epic 13-12 penalty shootout win over Ilves in the UEFA Europa League first qualifying round. He helped Shamrock Rovers keep six consecutive clean sheets in the remaining matches of the 2020 season, and the club finished the season unbeaten, winning the League of Ireland for a record 18th time. He also helped Shamrock Rovers beat Sligo Rovers 2-0 in the FAI Cup semi-finals to reach the final. In the FAI Cup final, the club lost 4-2 to Dundalk after extra time, failing to achieve a double. Mannus made twenty-two appearances in all competitions, keeping 13 clean sheets in 18 league games. He was awarded the SWAI Goalkeeper of the Year for 2020 and was named to the PFAI Premier Division Team of the Year. He ruled out retirement, aiming to play beyond 40, and subsequently signed a contract extension.

At the start of the 2021 season, Mannus started in the President of Ireland's Cup against Dundalk, where Shamrock Rovers lost 4-3 in a penalty shootout after a 1-1 draw. He helped the club maintain an unbeaten run in the first eleven league matches. In a match against Sligo Rovers on 10 April 2021, Mannus made an error, allowing a shot to slip through his fingers, leading to a 1-1 draw. Manager Stephen Bradley defended him, confident in his ability to bounce back. The club's unbeaten league run ended on 21 May 2021 with a 2-1 loss to Dundalk. Mannus played both legs of the UEFA Champions League first qualifying round against Slovan Bratislava, saving a penalty in the first leg, but Shamrock Rovers lost 3-2 on aggregate and were relegated to the UEFA Europa Conference League. He kept clean sheets in both legs of the third qualifying round against KF Teuta, as Shamrock Rovers won 3-0 on aggregate. However, Mannus played in both legs of the play-off round against FC Flora, where an error in the second leg contributed to a 5-2 aggregate loss and elimination. After a three-match losing streak, he improved his performance, helping Shamrock Rovers keep three consecutive clean sheets in the league between 10 September and 24 September 2021. On 29 October 2021, Mannus helped the club beat Finn Harps 3-0 to win the league for the second consecutive time. He made forty-three appearances in all competitions that season and signed a one-year contract extension.

At the start of the 2022 season, Mannus started in the President of Ireland's Cup against St Patrick's Athletic, saving a penalty in the shootout to help Shamrock Rovers win 5-4 after a 1-1 draw. He started the first five league matches, winning three. He missed one match due to illness but returned to the starting lineup in a 2-2 draw against Sligo Rovers on 18 March 2022. Following this, he helped the club achieve a thirteen-match unbeaten run. Mannus played eight times across the UEFA Champions League and UEFA Europa League qualifying rounds, which saw Shamrock Rovers qualify for the group stages of the UEFA Europa Conference League for the first time. In a 0-0 draw against Derry City on 12 August 2022, he kept a clean sheet and saved a first-half penalty. In a subsequent 3-0 win against Dundalk, Mannus kept another clean sheet and made several vital saves, including a second-half free-kick. His teammate, Aaron Greene, praised him as the best goalkeeper in the league, and manager Stephen Bradley noted his rejuvenated form. For his performance, he was named the club's Player of the Month for August. On 17 October 2022, Mannus made his 200th appearance for Shamrock Rovers against Drogheda United but was substituted in the 61st minute due to a knee injury. He made a quick recovery, returning for a 4-1 win against St Patrick's Athletic. Three days later, on 24 October 2022, Shamrock Rovers were confirmed as champions, winning their third consecutive league title. Mannus started the match against Derry City on 30 October 2022, keeping a clean sheet in a 1-0 win as the club lifted the trophy. He made forty-eight appearances in all competitions that season and signed another contract extension. He also won the SWAI Goalkeeper of the Year for 2022.

In the first two league matches of the 2023 season, Mannus received two late bookings for dissent. In a subsequent 2-1 loss against Derry City, he captained Shamrock Rovers. He helped the club keep three consecutive clean sheets in the league between 31 March and 10 April 2023. However, during a 2-0 win against Derry City on 1 May 2023, he suffered a dislocated finger and was substituted, an injury that kept him out for two months. He returned from injury on 27 July 2023, starting in a 4-0 loss against Ferencvárosi in the UEFA Europa Conference League second qualifying round. The club lost the return leg 2-0 and was eliminated. Following his return, Mannus regained his position as Shamrock Rovers' first-choice goalkeeper for the rest of the season. He helped the club keep four consecutive clean sheets in the league between 22 September and 27 October 2023. During this period, Mannus helped Shamrock Rovers beat Drogheda United 5-0 on 22 October 2023, securing their fourth consecutive league title. He made twenty-five appearances in all competitions during the 2023 season.

Mannus retired at the end of the 2023 League of Ireland Premier Division season, having won a record six League of Ireland titles and setting a club record of 128 clean sheets in 285 appearances for Shamrock Rovers.

7.1. Individual

• Ulster Footballer of the Year: 2007-08
• SWAI Goalkeeper of the Year: 2010, 2020, 2022
• League of Ireland Premier Division Most Clean Sheets: 2022
• PFAI Premier Division Team of the Year: 2010, 2019, 2020