Samir Nasri's chances of landing a permanent West Ham contract hang in the balance following another injury setback.

The former Arsenal midfielder joined the Hammers on New Year's Day as a free agent having spent over a year out of the game due to a doping ban.

Nasri signed an initial six-month deal in the hope of earning a two-year contract, but a series of niggling injuries have limited him to just three Premier League starts.

The Frenchman was due to come on as a substitute at Chelsea on Monday night, only to suffer a calf injury while warming up which will rule him out of this weekend's trip to Manchester United.

Manager Manuel Pellegrini has now admitted signing Nasri was a gamble and cast doubt on whether he will be offered a permanent deal.

"About next season, I don't know," said Pellegrini.

"We knew that when Samir came here we had a risk for muscle injuries because he was more than one year without playing, so we will see at the end of the season."

There was brighter news on another ex-Gunners midfielder, Jack Wilshere, whose season has been wrecked by ankle problems.

The former England international played for the club's under-23s on Monday, his first action since a brief substitute appearance in December.

"Wilshere is almost ready," added Pellegrini. "He played for the under-23s and will play another one, then after that he will work with us."

Pellegrini has been frustrated by injuries all season, with as many as 10 players on the casualty list at one point or another.

West Ham's campaign is in danger of fizzling out into mid-table mediocrity and Pellegrini is expected to clear the decks in the summer.

"The ambition is to always improve," he said. "It is hard to put in a target before the start of the season.

"This season we have played good games, we have changed a lot of things but we haven't been able to play with all the players we wanted this season.

"The next season our target must be to improve on this one."