Portuguese Espirito Santo, who was fired by Nottingham Forest this month, joined West Ham after it made a dismal start to the Premier League campaign, losing 3-0 to promoted Sunderland on the opening day before suffering heavy defeats by Chelsea and Tottenham Hotspur.

Potter's final game was a 2-1 home loss to Crystal Palace last weekend amid fan protests, but the axe did not fall immediately, with the Englishman fulfilling club media duties ahead of this weekend.

"My objective is to work hard to get the very best from the team and ensure that we are as competitive as we possibly can be," Espirito Santo said.

"The work has already started and I am looking forward to the challenge that is ahead."

Espirito Santo had guided Forest through a relegation battle when he joined in December 2023 before exceeding expectations by taking it into the UEFA Europa League by finishing seventh last season.

But the former Wolverhampton Wanderers and Tottenham Hotspur manager admitted last month that his relationship with the club's owner Evangelos Marinakis had broken down.

He will take charge of his first game when West Ham faces Everton away on Tuesday (AEST).

The Hammers will be up against their former manager David Moyes, who left in 2024 despite leading the club to the UEFA Conference League title, the first major silverware won by the club for 43 years.

Under Potter, West Ham conceded 13 goals in the opening five games to hold the worst defensive record and as a result sits 19th in the Premier League while it was also knocked out of the Carabao Cup by Wolves last month.

"Results and performances over the course of the second half of last season and the start of the 2025-2026 season have not matched expectations," a statement fro West Ham read.

"The Board of Directors believe that a change is necessary in order to help improve the team's position in the Premier League as soon as possible."

Potter was appointed by West Ham in January to replace Julen Lopetegui, but the club won only five Premier League games under the 50-year-old Englishman last season to finish 14th.

"I am incredibly disappointed to be leaving West Ham, particularly without being able to achieve what we set out to achieve at the start of our journey in East London," Potter said via a statement.

"I do, however, fully acknowledge that the results have just not been good enough up to now."

The club lost a number of experienced players in the summer transfer window, with Aaron Cresswell, Vladimir Coufal, Danny Ings, Michail Antonio and Kurt Zouma departing.

Forward Mohammed Kudus joined London rival Spurs in a deal worth around £55 million ($112.6 million).

West Ham invested only £70 million ($143.3 million) on its squad, with full back El Hadji Malick Diouf, goalkeeper Mads Hermansen and striker Callum Wilson among the acquisitions.