Slaven Bilic and West Ham have parted company, with sources close to the club telling ESPN FC that David Moyes is set to be appointed in his place.
The club dropped into the Premier League's bottom three following a 4-1 defeat against Liverpool on Saturday and Everton's victory against Watford and a source said following that game that Bilic was expected to be fired.
West Ham have only won two of their 11 Premier League games so far this season, despite making significant additions over the summer including Joe Hart, Pablo Zabaleta, Marko Arnautovic and Javier Hernandez.
In a statement on their official website, they said: "West Ham United can confirm that Slaven Bilic has today left his position with the club.
"The chairmen and board of West Ham United would like to place on record their thanks and gratitude to Slaven and his team for their services over the past two-and-a-half years, but believe a change is now necessary in order for the club to move forward positively and in line with their ambition."
Bilic also had a statement on the club's website, saying: "I am sad that it hasn't worked out in the way we wanted this season. But I leave with my head held high, along with some wonderful memories that I will always cherish.
"I was confident that we would be able to progress this season and continue to close the gap between expectation levels and reality, but unfortunately it has not been the case.
"I believe in my qualities and wanted desperately to fight on to turn things around, but I understand the club's desire to make a change."
Bilic, who was appointed in June 2015, led the club to a seventh-place finish in the Premier League during his first season in charge and 11th last season.
Joint chairmen David Sullivan and David Gold said they had made the decision to dismiss Bilic "with disappointment and heavy hearts," writing on the club's official website: "During the summer, the board invested heavily signing the players Slaven believed would complete the squad he needed to push the club back towards the level we had reached in his first season, and we believe we have the players capable of doing that.
"Sadly, performances and results have not been of the expected standard and, in recent weeks, we have not seen enough indication of the required improvement to give us the encouragement that things would change and we would meet our Premier League aspirations this season."
They added: "We see this as an exciting opportunity to appoint a quality manager to the position to inject fresh ideas, organisation and enthusiasm into a very talented squad.
"We will now focus our entire efforts on bringing in the manager we believe can get the best out of the current squad of players and steer the club towards the top half of the table as quickly as possible."
As first reported by ESPN FC on Saturday, former Everton, Manchester United and Sunderland manager Moyes has been identified as Bilic's replacement.
Sources said on Monday that Moyes, who has been doing punditry work in Qatar, agreed the deal on Sunday night and was due to fly to London later in the day to finalise terms.
Asked on Sunday if he would be keen on the role, he told beIN Sports: "I'm interested, but until that vacancy comes available, and at the moment it's not available... I know what Slaven is going through, and he must be hating it and wanting to get a result as quickly as possible.
"If it comes available yes, and at the moment it's not available. Unfortunately for me to get back in [to club management] means a manager would have to lose his job, and I wouldn't wish that on anybody."
Sources also said West Ham are ready to approach former England defender Stuart Pearce to join Moyes' staff once he is confirmed as Bilic's replacement.