Arsene Wenger  defended Theo Walcott  for his gesture towards Tottenham  supporters during the north London derby but the Arsenal  manager hs sweating on the forward's fitness after he was forced off with a knee problem.The England international was carried off on a stretcher late on in the Gunners' 2-0 victory in the FA Cup third round at the Emirates Stadium on Saturday and Spurs fans appeared to throw missiles at the 24-year-old after he used his hands to signal the scoreline to visiting supporters behind the goal.Wenger defended Walcott and claimed that the England international should not face repercussions from the FA for antagonising the Spurs fans."The doctor said to me that coins had been raining over his head and maybe that's why he did that," the Frenchman told reporters."After that, what he did was not offensive. It's a reaction that didn't offend anybody. I have seen the pictures and I think it doesn't even look aggressive, he is smiling."Of greater concern to Wenger will be the knee injury that forced Walcott off and meant that the Gunners had to play the final minutes of the game with just 10 men.Wenger confirmed that Nicklas Bendtner is expected to miss four weeks with an ankle injury, while club medical staff will now assess Walcott to establish "whether it was a stretched ligament or a kick".Olivier Giroud missed the Spurs clash through illness and the Arsenal manager admitted that he could be forced to accelerate his plans to sign a striker in the January transfer window."I am waiting to see now who walks out there and knocks at the door, waiting to come in," he added.