Mesut Özil will miss at least three weeks with a hamstring injury.
Özil was in the starting lineup in Arsenal's Champions League loss to Bayern Munich and was substituted at halftime after not appearing right.
"He has a hamstring problem that looks quite serious," said Arsène Wenger. "We have to make a scan to see how bad it is but he is out at least for a few weeks. I hope it's not too bad."