Arsenal boss Arsene Wenger admits Theo Walcott could be their matchwinner in tomorrow night's Champions League semi against Manchester United.

"We looked more comfortable with 4-4-2 and it looked more threatening, but it also depends on who is available," the Arsenal manager said.

"However, when you play [Theo] Walcott on the right you play more 4-3-2-1.

"He is a winger not a midfielder, so you have to balance the side to be a bit more defensive.

"Also, when [Cesc] Fabregas plays behind the striker, the striker looks to be a little isolated so you have to get the balance of the team right."

England forward Theo Walcott, Bacary Sagna and Alex Song - who dropped back to the centre of defence - were the only survivors from Old Trafford.

Wenger maintains 20-year-old Walcott will be one of his key weapons again on Tuesday.

"I wanted to win the game against Portsmouth, and when you are 19 or 20 years old you can recover in three days," he said.

"I gave Theo a good breather and took him off with 25 minutes to go. That was just perfect for him and he will not be fazed on Tuesday night."