Arsenal boss Arsene Wenger admits they could be missing Mathieu Flamini for their Champions League tie this week.
Flamini was forced off during victory over Norwich City.
"He had concussion. 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," explained Wenger.
