Birmingham City FC announced the dismissal of its coach, Wayne Rooney.
Rooney won just two of his 15 matches in the tournament, which saw the club drop from sixth to twentieth in the table.
First team coach Karl Robinson was also sacked.
A club statement said: “Birmingham City has today parted ways with technical director Wayne Rooney and first-team coach Karl Robinson.”
“Despite their best efforts, the results have not met the expectations initially expressed. The Board of Directors therefore believes that a change in management is in the best interest of the club.
“The club’s board and management are fully aligned and will continue to drive transformation and take bold steps to rebuild Birmingham City into the organization its fans and community deserve.
“The Board would like to place on record its sincere thanks to Wayne and Carl for all their efforts.”
Rooney said in a statement: “I would like to thank Tom Wagner, Tom Brady and Gary Cook for giving me the opportunity to coach Birmingham City and the support they have given me during my short time with the club.”
He added: “Football is about creating results, and I realize they were not at the level I wanted them to be. However, time is the most precious commodity a manager needs, and I don’t think 13 weeks was enough to oversee the changes required.
“On a personal level, it will take time to get over this setback. I have been involved in professional football, as a player or manager, since I was 16. Now, I plan to spend some time with my family as I prepare for the next opportunity in my journey as a manager.
“Finally, I wish Birmingham City and its owners our best wishes as they pursue their ambitions.”
What we can glean from Wayne Rooney's first two coaching spells
Birmingham chief executive Gary Cook added: “We are committed to doing what is necessary to achieve success at St Andrews.
“Unfortunately, Wayne's time with us did not go as planned and we decided to move in a different direction.
“The search for a successor begins with immediate effect and we will update fans when we have more news.”
It has been confirmed that professional development coach Steve Spooner will take over on an interim basis until a permanent successor is found.
Birmingham's new owners sacked Rooney's predecessor John Eustace last October, despite an impressive start to the season, citing the need for a “winning mentality” and a “culture of ambition”.
Rooney (38 years old) was appointed when Birmingham was in a promotion playoff position after collecting 18 points from the first 11 matches in the tournament.
But a poor run of results, which included nine league defeats, has left Birmingham eyeing a potential relegation battle, sitting just two places above the relegation zone.
Eustace, 44, left when Birmingham were sixth in the table and followed a season in which he led them to their highest points total since 2016 as they avoided relegation despite off-field uncertainty over the club's ownership.
US-based Shelby Companies Limited completed its takeover of St Andrew's in July, with NFL legend Tom Brady announced as a minority investor in August.
Rooney previously spent 19 months at the helm of Derby County, but was unable to prevent their relegation to the top flight in 2022 after a 21-point deduction and the club spent almost the entire 2021-22 season in management.
The former Everton and Manchester United striker also spent 15 months at the helm of Major League Soccer side DC United, but left by mutual consent in October after failing to qualify for the play-offs.
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(Mark Atkins/Getty Images)
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