LONDON (AFP) Arsene Wenger has slammed Birmingham defender Liam Ridgewell for the tackle which left Arsenal winger Theo Walcott nursing a potentially serious knee injury. Walcott was forced off before half-time in the Gunners 3-1 win over City at the Emirates Stadium on Saturday following a hefty tackle from Ridgewell. The England international was left in a crumpled heap after the defender crashed into him, winning the ball but also crunching into the back of his legs. Walcott played on for another 20 minutes before being withdrawn and will undergo a scan on Sunday to determine the extent of the injury. Wenger has ruled out the possibility of cruciate ligament damage but fears Walcott might have twisted his medial ligaments, which would rule him out of Tuesdays Champions League game with AZ Alkmaar and could leave him facing several weeks on the sidelines. He has a bruised knee and its swollen, Wenger said. Its difficult to assess and know whether it is a twisted medial ligament or just a kick. He said he was unstable when he was running which is not good news. We will assess on Sunday morning when he will have a scan - if its just a kick then he should he available for Tuesday, if its a twist then he wont be. I believe, personally, he will not be available for Tuesday, at least. It was a cut-through tackle, without any restriction. It was meant to impress. It looked quick and hard from outside - I dont know if he didnt want to play the ball. The incident was a grim echo of the last occasion these sides met, when Arsenal striker Eduardo suffered a compound fracture of his leg following a tackle by Martin Taylor. That said, the implications for Walcott should not be nearly as severe as they were for the Croatia striker, and Birmingham manager Alex McLeish was justified in pointing out that the referee, Lee Probert, did not even see fit to award a free-kick for Ridgewells tackle. Arsenals sensitivities were doubtless heightened by the memory of what happened after that infamous meeting with Birmingham in 2008, when their title challenge imploded. But Wenger was understandably heartened by his side stretching their winning streak to seven games in all competitions. The north Londoners were in control from the 16th minute, Robin van Persie collecting Alex Songs pass and whipping a shot into the far corner, and when Abou Diaby doubled the advantage moments later, Birmingham appeared set for a long day. But they were handed an unexpected lifeline when Vito Mannone, the young Italian goalkeeper, inexplicably flapped at a high ball and Lee Bowyer volleyed in. Wenger was unimpressed with both that error, hinting afterwards that Manuel Almunia could win back his starting place against Alkmaar. The killer blow was finally applied in the 84th minute, when Andrey Arshavin curled in a low shot following a swift counter-attack. We were cruising and in control at two goals, he said. We were wondering who would score the third but we started making mistakes. We didnt have the same fluency, control or pace in the second half. McLeish issued a warning to his own side after this latest defeat, suggesting that they could be running out of chances to impress before the opening of the winter transfer window. We need to find that cutting edge and we are looking for our match winners to play consistently well, said the Scot, who is expected to be handed 40 million pounds to spend by Citys new owner Carson Yeung.