Manager Manuel Pellegrini has left West Ham with immediate effect, the club have announced.
The news came within hours of their 2-1 loss to Leicester at the London Stadium, a defeat which leaves the Hammers just a point above the relegation zone in 17th place.
It was a fourth straight home defeat and a ninth loss from their previous 12 games.
The former Manchester City manager departs after 18 months in charge, having been appointed in May 2018 on a three-year deal.
West Ham United can confirm that Manuel Pellegrini has left the Club with immediate effect.— West Ham United (@WestHam) December 28, 2019
A West Ham statement read: "Joint-Chairmen David Sullivan and David Gold, along with the board and everyone at West Ham United, would like to place on record their thanks to Manuel for his service over the past 18 months."
Sullivan said: "It is with great disappointment that we've had to make this decision. 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.
After defeat to Leicester, the Chilean was asked about his future at the club. He said: I am confident. I have a lot of experience of being in this position.
"When you don't get the result people talk about you being sacked. For me I only worry about managing games."
The Hammers face Bournemouth on New Year’s Day.