Arsenal's Theo Walcott is expected to be out for a month with a knee injury he sustained in Saturday's FA Cup third round win against Tottenham.

Walcott's injury may force his manager Arsene Wenger to make a move for a new striker in the transfer window.

Widespread reports in Monday's newspapers suggested Walcott will face a lengthy spell on the sidelines after he was stretchered off following his impressive performance as Arsenal's lead forward, filling in for the injured duo of Olivier Giroud and Nicklas Bendtner.

"Theo has a knee problem," Wenger said after the game on Saturday. "We don't know if it is a stretched ligament or just a kick, he got two kicks on his knee.

"We still have [Lukas] Podolski and [Mesut] Ozil on the bench. [Olivier] Giroud was sick, he was not injured, so for the next game he should be available. Of course if we lose Theo for a longer period, it is a problem."

Bendtner is also expected to be out for around a month after injuring his ankle against Cardiff on New Year's Day, leaving Arsenal alarming short of striking options heading into a condensed period of action that will include crucial Premier League, FA Cup and Champions League games.

Walcott was reported to be due for a scan on his injured knee on Monday, with the results likely to be crucial in Wenger's transfer plans for the next few weeks.

However, the Arsenal boss has again warned it will be difficult to seal deals for top players in this mid-season transfer window.

"I said many times we don't rule anything out, but you know as well that all the big players are at big clubs at the moment and they go for important targets," Wenger said. "We are like everyone, we look out there and see what is happening, if an opportunity turns up. Unless you have a club in a desperate financial situation it will be difficult."

Meanwhile, Jack Wilshere has expressed his hope that his Walcott will not face disciplinary action after he taunted Tottenham fans by reminding them of the score line as medical staff carried him off.

Wilshere was given a two-match ban by the FA for an offensive gesture towards Manchester City supporters last month, but he hopes the jovial nature of Walcott's repost to his detractors will be taken into account.

"I think they [Spurs fans] were giving him a bit of stick and he responded. He's a bit smarter than me, I suppose," Wilshere said. "It is football. They were giving it to him and got it back. People have to look at it as a bit of banter."