Lukas Podolski has been ruled out for three weeks after suffering a hamstring injury in Arsenal's Champions League triumph over Fenerbahce on Tuesday evening.
The German forward was forced off the pitch early in the second half and he will now miss the derby clash with Tottenham Hotspur on Sunday afternoon.
"We paid a heavy price on the injury front because we lost Podolski," Wenger told reporters.
"Podolski's definitely out for 21 days."
The 28-year-old will also miss Germany's World Cup qualifiers against Austria and the Faroe Islands.