The England striker sustained the injury during Arsenal's 5-2 derby win over Tottenham at the weekend but was able to play on and scored the Gunners' fifth goal in injury-time at the end of the match.
Arsenal boss Arsene Wenger revealed Walcott had not trained on Tuesday and would have a scan to determine the extent of the injury although he thought it would be short-term.
Gervinho is back in the squad for the Emirates Stadium tie.
Source: PA
Source: PA