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 tomorrow. 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."

The incident brought back memories of Martin Taylor's X-rated challenge on Eduardo at St Andrew's during February 2008, which left the Croatia striker with an horrific double leg fracture and out of the game for almost a year.

After that match, Wenger had lambasted the Blues defender whom, in the heat of the moment, he claimed "should never play again", a statement later retracted.

This afternoon, the Arsenal manager felt it was difficult to judge just how much intent Ridgewell put into the challenge, which referee Lee Probert had not given as a foul.

"It was a tackle which cut through, without any restriction," said Wenger. "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."

By the time Arsenal lost Walcott, they were already 2-0 ahead through Robin van Persie and Abou Diaby.

However, Lee Bowyer capitalised on a mistake by young keeper Vito Mannone - preferred to fit-again Manuel Almunia - to pull a goal back before half-time.

After soaking up plenty of pressure from the battling Blues, substitute Andrey Arshavin wrapped up the points with a well-taken strike five minutes from time to make it seven successive wins in all competitions.

"We were crushing, in control, and wondering who would score third goal," said Wenger, "but we made a mistake defensively and they got a goal back. The Premier League is like that.

"In the second half, we did not have the same fluency, control, or pace.

"However, 3-1 is still a fair result because we still had plenty of chances.

"Birmingham worked hard and regrouped well when they did not have the ball.

"We also lacked a bit of sharpness and sometimes tried to force a situation individually when it was possible collectively, and that is why we did not score more goals."

Wenger added: "When we focus to play our game, I believe we can score and play the ball through any space.

"That is something fantastic, but we have to keep our composure."

New Birmingham owner Carson Yeung has promised McLeish a transfer kitty of up to £40 million to spend in January, and was in the stands at Emirates Stadium this afternoon.

The Blues boss hopes this is the start of a bright era for the midlands club.

"Maybe people will inflate prices and we have to be careful, but we welcome it, because we need some fresh quality in the team," the former Rangers manager said.

"It is a challenge to our guys now."

McLeish added: "We are where most people expected us to be in the league, but performances have been good and I do not think have looked out of place.

"We just have lacked a cutting edge in not converting our chances. We need to find it.

"Now I am looking for our match winners to be playing consistently well and show they can go to the next level."