Tomas Rosicky is facing at least two weeks on the sidelines after suffering a hamstring injury against Sevilla.
Arsenal's Czech Republic international midfielder was substituted four minutes into the second half of the Gunners' 3-0 UEFA Champions League victory.
Arsene Wenger confirmed the playmaker had suffered another hamstring problem but the full extent of the damage is still to be revealed.
Wenger told the club's official website: "We have bad news for Rosicky because he is a player I like to have in the side.
"He has done his hamstring again. I don't know yet [how serious it is], we have to wait 48 hours, but he will be out at least two weeks."
Rosicky told his personal website: "I don't know yet the seriousness of the injury, the doctors will tell me that on Friday.
"But when I felt a pull in my muscle, I knew immediately I had to leave the pitch."