Jack Wilshere has been left "very upset" by his latest injury setback with the West Ham midfielder facing up to six weeks on the sidelines.

The 26-year-old underwent ankle surgery on Monday in London after missing last weekend's 3-1 victory over Everton.

Wilshere's career has been punctuated by a series of injuries, and Hammers boss Manuel Pellegrini revealed that his latest problem has been tough for the player to accept.

"He was working so well that of course he was very upset about what happened," Pellegrini said. "I spoke with him before he started the week. He felt the pain in his ankle.

"He is a player, who is maybe not too old, but he has a lot of experience with injuries. I hope he will know what is the best way to recover as soon as he can."

Wilshere arrived at the London Stadium in July after ending his 17-year association with Arsenal, and having been omitted from Gareth Southgate's England World Cup squad.

The former Gunners midfielder, who signed a three-year deal at West Ham, started the opening four matches of the season, but, following a complication with a screw in his ankle from a previous operation, missed their first league win of the campaign last Sunday.

Pellegrini added: "The club doctor can say more about it than me, but he has a screw in his ankle from surgery he had some years ago.

"Maybe it made some movements so they had to take the screw out. We will see how many weeks he is out for."

Pellegrini will also be sweating over the fitness of forward Marko Arnautovic ahead of their London derby against Chelsea on Sunday.

Arnautovic, who has netted three times in the Premier League this season, was substituted in the second half at Goodison Park.

"Marko finished with a problem in his knee, and he has had some treatment," Pellegrini added. "We will see if he is fit for Sunday.

"He played very well in that game against Everton and, we hope he will have recovered for the next game."