Flamini suffered a concussion in Saturday's 4-1 Premier League win over Norwich, and although the Group F clash is vital in their potential progress to the last 16, he will not be risked.
Wenger said: "Flamini is doing well, has practiced normally, but we will not play him tomorrow.
"There is a five-days (concussion) rule that we will respect, not to take any chance. It was a concussion and the doctor advised us not to play him. He will be okay for the weekend.
"I'll leave myself 24 hours until tomorrow afternoon to decide the team."
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