Manuel Pellegrini's 18-month reign as West Ham United manager ended abruptly on Saturday as the Chilean was sacked shortly after his side's 2-1 home defeat by Leicester City in the Premier League.
The defeat left West Ham fourth from bottom, just one point above the relegation zone after a dreadful run of form.
Former Manchester City title-winning manager Pellegrini, who steered the team into the top four earlier in the season, had already given his post-match news conference at the London Stadium and had not hinted at what was about to follow around 15 minutes later.
West Ham broke the news in a statement on its website.
"It is with great disappointment that we've had to make this decision," joint-chairman David Sullivan said.
"Manuel is a gentleman and it has been a real pleasure to work with someone of his calibre. However, it has become clear that that a change is required to get the club back on track in line with our ambitions this season.
"We felt it was necessary to act now in order to give the new manager as much time as possible to try and achieve that."
West Ham spent around €80 million ($104.62 million) in the summer transfer window on the likes of striker Sebastien Haller and Pablo Fornals.
They began the season well, going on a six-match unbeaten streak after losing to Manchester City on the opening day.
But since beating Manchester United at home on Sept. 28 they have won only twice in their last 13 league games, but none at home.
West Ham looked woefully low on confidence against a Leicester side showing nine changes to the line-up beaten by Liverpool 48 hours earlier but who were still far too good for the hosts.
Fans made their frustrations clear on Saturday, jeering Pellegrini's substitutions of Haller and Manuel Lanzini.
"I understand the fans, they deserve better results and deserve a better performance of the team," Pellegrini said in his final post-match news conference.
West Ham face a crucial home match against fellow strugglers Bournemouth on New Year's Day.