Arsenal secured another impressive win against Norwich City at the weekend to remain top of the Premier League but the victory may have come at a cost with influential midfielder Mathieu Flamini picking up an injury.

The French midfielder has been a revelation since returning to the club on a free transfer this summer, providing a solid base from which the likes of Mesut Ozil, Aaron Ramsey and Jack WIlshere have flourished.

Flamini was forced off during the 4-1 win over Norwich following a clash of heads that led to him suffering from concussion and Wenger admitted that he may not be available for the clash with Borussia Dortmund in the Champions League on Tuesday.

"He had concussion," revealed Wenger after the game. "He had double vision, so on the advice of the doctor I took him off because I did not want to take any gamble.

"I don't know if he'll be available for Dortmund, it depends now what the doctors will decide. Sometimes they are not allowed to play for five days, it depends how big the concussion was."

While Arsenal await the doctor's verdict on Flamini, it seems they will definitely be without Theo Walcott for the Champions League tie with Dortmund after the England winger suffered a setback on his road to recovery.

Walcott had minor surgery which ruled him out of England's recent World Cup qualifiers but had returned to full training with the north London club.

However, his stomach injury would once again flare up in training and Wenger admitted the winger would likely miss the next three games.

Wenger told the Mirror: "He had a setback. He had to stop, to jog again, I don't think we will see him against Dortmund, nor Crystal Palace nor Chelsea. He is at least two weeks away now."

Walcott had originally been ruled out until the start of November but he had been making good progress and was hoping to return far earlier in order to help Arsenal maintain their impressive start to the season.

Despite the absence of Walott, and possibly Flamini, Wenger will be hoping that Arsenal can continue their good form against last season's Champions League finalists.

The Gunners were particularly impressive when beating Napoli 2-0 at the Emirates and will be confident of picking up another win against Dortmund in order to maintain their perfect start to this season's Champions League campaign.