London - Arsenal manager Arsene Wenger said Tuesday he was prepared to take a "risk" on the future of Theo Walcott as injury ruled the unsettled England forward out of the Champions League tie with Montpellier.Walcott will miss Wednesday's match at the Emirates Stadium with a shoulder injury suffered during Arsenal's 5-2 North London derby win over Tottenham Hotspur in the Premier League in Saturday, where he played on and scored the Gunners' fifth goal in extra time at the end of the match.He is now due to undergo a scan although Wenger said he expected Walcott to be sidelined for only a brief spell."The injury he got during the game with his shoulder, we have to scan that today and see if there is no damage," Wenger said Tuesday."He will be out for tomorrow (Wednesday). It should be short-term."We will miss (Andre) Santos as well, who has a muscle strain in his abdomen. The two players coming in the squad are Gervinho and (Kieran) Gibbs."Walcott, 23, has yet to agree a new contract with Arsenal and, as a consequence, could leave at the end of the season on a free transfer, becoming the latest front-line player to quit the Gunners in recent times but without the club receiving any financial benefit.One way to avoid the lack of a cash return on Walcott, who joined the Gunners for £5m in January 2006, would be to sell him during the upcoming January transfer window.But veteran French manager Wenger has insisted Walcott will be going nowhere in January and is prepared to take the risk of him leaving for nothing."There's a risk, yes, but that we are ready to take," explained Wenger, who has come under fire from some Gunners fans for presiding over the club's ongoing seven-year trophy drought, having previously brought 11 major honours to the club following his appointment in 1996."A successful season is more important for us than this risk that is only a financial risk, apart from losing the player," Wenger insisted."If we sell him, we lose him anyway."I believe that we started the season with this squad and we want to finish the season with this squad."What is important is what we achieve together for the season - to do that I just think that Theo is a big part in that."Arsenal's victory over Spurs was a perfectly-timed confidence boost because the Gunners can't afford a slip-up against Montpellier.Arsenal lie second in Champions League Group B, one point behind Schalke, and failure to beat the French champions could leave Wenger's men facing a tricky must-win tie at third placed Olympiakos in their final match.But, with Schalke hosting Olympiakos, victories for Arsenal and the German club this week would guarantee their places in the knockout stages.Bottom of the group Montpellier haven't won in their last four matches and cannot qualify for the last 16.Wenger said only by maintaining the same mental approach they showed against Spurs could Arsenal hope for a similar result on Wednesday."It is important on the back of the Tottenham game we show another good performance and a resolute attitude."Montpellier had a slow start to the season, but they have rediscovered their balance over the last few months and they played very well against Paris St Germain."It should be an open game because a draw is not good for either side."