Cesc Fabregas has been ruled out of Arsenal's Champions League clash against Celtic midweek with a hamstring injury, the Premier League club confirmed on Tuesday.
The Gunners captain could, however, return for Saturday's Premier League trip to Manchester United.
Both Abou Diaby and Aaron Ramsey are in contention on Wednesday as the Gunners look to defend a 2-0 lead, with manager Arsene Wenger set to rotate his side.
Czech winger Tomas Rosicky has returned to training following a hamstring problem and could be match fit by the weekend.
However, England forward Theo Walcott (back), reserve goalkeeper Lukasz Fabianski (knee), France winger Samir Nasri (broken leg) and defender Johan Djourou (knee) all continue their rehabilitation.