Arsenal forward Theo Walcott faces another spell on the sidelines after suffering a knee injury in their 3-1 win over Birmingham City.

The England forward was making his first start of the season for the Gunners, having been sidelined since August because of a back problem.

However, following a strong, sliding challenge by Blues defender Liam Ridgewell, Walcott eventually hobbled out of the action just after the half-hour.

Walcott will undergo a scan to assess the damage, which could now signal another spell on the sidelines for the World Cup hopeful.

"It is difficult to assess at the moment, whether it is a ligament which is twisted or just a kick," said Wenger.

"The fact he says he felt a little unstable when he was running is not good.

"We will scan him on Sunday. If he has just a kick, then he has a chance to play on Tuesday (away to AZ Alkmaar).

"But I believe he will not be available. It is not a cruciate problem, but it could be more than a week."

On Ridgewell's involvement, Wenger added: "It was a tackle which cut through, without any restriction.

"I felt it was a tackle meant to impress. I do not know whether he wanted to play the ball. If he touched just the ball, then that is part of the game. That is my first impression from the bench, but I would have to see it again." Birmingham manager Alex McLeish felt there was little wrong with Ridgewell's challenge.

He said: "It was a fierce defender's tackle.

"Liam must have caught Walcott because he stayed down and got treatment, but I don't know whether it was dangerous. There was no free-kick given. If you are going to penalise every tackle, it would be a different game."