West Ham United's Chilean manager Manuel Pellegrini gestures at The London Stadium on Saturday. Ben Stansall/AFP
West Ham sacked manager Manuel Pellegrini after Saturday's 2-1 home defeat to Leicester left the Hammers just one point above the Premier League's relegation zone in 17th.
A run of just two wins in 14 games, including seven defeats in their last nine league matches, saw patience run out with the 66-year-old former Real Madrid and Manchester City boss.
"It is with great disappointment that we've had to make this decision," West Ham joint-chairman David Sullivan said in a club statement.
"Manuel is a gentleman and it has been a real pleasure to work with someone of his calibre.
"However, it has become clear 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 goal."
West Ham host Bournemouth, who sit one point and one place above them in the table, on January 1.
Pellegrini has failed to provide enough of a return on a significant transfer spend over the past 18 months with over £100 million ($130 million) splashed on the likes of Felipe Anderson, Sebastien Haller, Pablo Fornals, Andriy Yarmolenko and Issa Diop.
West Ham overcame a difficult start to finish 10th in Pellegrini's first campaign in charge and began this season brightly.
After an impressive 2-0 win over Manchester United in late September the Irons sat fifth in the table.