Tony Pulis has left his position as Crystal Palace manager, plunging the club into turmoil just a day before it starts the English Premier League season.
Pulis walked away late on Thursday, but Palace wouldn't confirm it until Friday, and said it was by "mutual consent."
Keith Millen, the assistant manager, will take temporary charge of the team for the match at Arsenal on Saturday.
Arsenal manager Arsene Wenger, the longest serving manager in the league, was as stunned as the rest of English football.
"I was at a managers' meeting on Monday with Tony Pulis, and nothing indicated that he would not be here (on Saturday) afternoon," Wenger said on Friday.
"It was a complete surprise to me, and what kind of consequence that will have on Crystal Palace, I don't know."
British media reported that Pulis grew frustrated at the club's lack of transfer activity this offseason, and had a deteriorating relationship with Palace co-chairman Steve Parish. They talked on Thursday after practice.
Palace signed just four players, including Martin Kelly from Liverpool on Thursday, at a combined reported cost of around 2.5 million pounds ($4.2 million). The others were Fraizer Campbell from Cardiff City, and the free transfers of Brede Hangeland from Fulham, and Chris Kettings from Blackpool.
Pulis kept Palace in England's lucrative top division last season despite the team having just four points from 11 matches and lying in last place when he was hired in November.
"He made a miracle," Wenger said.
That achievement earned Pulis the award as the Premier League manager of the year, and maintained his record of never having been relegated in his 22 years as a manager.
"The club would like to thank Tony for his efforts with the club during last season and wish him all the best for the future," Palace said in a brief statement on its website.
Malky Mackay has become the leading candidate to replace Pulis, as he had a close relationship with club sporting director Iain Moody. They were both at Cardiff last season. Millen managed Bristol City, but Saturday's game will be his first managerial experience in the Premier League.