Arsenal boss Mikel Arteta admits an injury suffered by captain Martin Odegaard is a concern.
The Gunners captain pulled up before yesterday's 1-1 draw with Nurnberg.
Arteta said: "He felt something in the warm up.
"I think it was his calf. He got a knock there and he wasn't feeling good enough to play. And Leo (Trossard) as well had an issue.
"They are struggling and we had other players with issues picked up in the week so we have to be cautious. It's pre-season and some of them have only had two or three training sessions so we'll take it step by step."