Walcott and Oxlade-Chamberlain
Arsenal midfielder Alex Oxlade-Chamberlain (L) faces fitness testsGetty

Arsenal manager Arsene Wenger says the club does not know how long Alex Oxlade-Chamberlain will be out of action after recent reports suggested the midfielder could be ruled out for up to four weeks.

The England international was forced to leave the ground early in the second half of Arsenal's FA Cup victory over Manchester United on 9 March.

Wenger confirmed the midfielder suffered a hamstring strain but refused to say whether he will miss the Premier League game against West Ham United on 14 March and the crucial Champions League second leg with Monaco on 17 March.

"Chamberlain has a hamstring strain, the only thing we don't know is how bad it is because usually the scans are only done 48 hours after the accident. That will be done today [Wednesday]," the manager said.

Meanwhile, the French boss claimed Mathieu Flamini is ready to return to action against the Hammers, while Jack Wilshere and Gabriel Paulista are progressing well from their respective problems and will be playing again soon.

"Mathieu is training, he could be available for the squad on Saturday," Wenger said. "Jack is progressing well, he is not back in training yet.

And speaking about Paulista, who missed the FA Cup game with United following his injury during the win over Queens Park Rangers, the Arsenal manager said: "Gabriel may be [available] next week, he should come back into training on Sunday or Monday."

Furthermore, the manager suggested he will not rest a lot of key players for the London derby despite the Gunners facing Monaco in the crucial Champions League tie three days later.

He said: "No. We were at a high level of fatigue because we played against Monaco, Everton, QPR, Manchester United, all very physical games. I will have to test medically, physically, how the players are on Friday, and I will make my decision then. The big priority is of course West Ham."