The former Everton man was taken off the field on a stretcher after colliding
with Liverpool's Jordan Henderson and was later ruled to have suffered a
concussion, which will keep him out of action for at least a week.
Wenger also revealed that the Gunners will be missing Abou Diaby and Yossi
Benayoun, while Tomas Rosicky is doubtful for Tuesday's match, which sees
Arsenal enter with a 4-0 deficit from the first leg in Milan.