Harry Redknapp, 67, has resigned as Queens Park Rangers manager to go undergo knee surgery.
Redknapp's decision was "accepted by the board" on Tuesday morning (3 February), the day after the January transfer window closed.
Les Ferdinand and Chris Ramsey have taken temporary charge of the club.
A statement from Redknapp read: "I have had such a fantastic time at QPR. I would like to thank the Board, the players and all my staff, and especially the supporters who have been absolutely fantastic to me since I arrived at the club for their tremendous support.
"Sadly I need immediate surgery on my knee which is going to stop me from doing my job in the coming weeks. It means I won't be able to be out on the training pitch every day, and if I can't give 100 per-cent I feel it's better for someone else to take over the reins.
"My relationship with Tony Fernandes has been one of the highlights of my footballing career and I wish the club every success. I am confident they will survive in the Premier League this year."
QPR currently sit second from bottom in the Premier League.
Redknapp replaced Mark Hughes as QPR boss in November 2012 but was unable to prevent relegation to the Championship at the end of the 2012/13 season.
He led the club back to the Premier League the following season, guiding the R's to a playoff victory over Derby County in May 2014.
QPR chairman Tony Fernandes added: "I would like to take this opportunity to thank Harry for everything he has done for QPR during his time in charge.
"We part on good terms and I would personally like to wish him all the best for the future."
Ferdinand, who held the position of Head of Football Operations at Loftus Road, will oversee first team duties ahead of Saturday's Premier League clash with Southampton.