Theo Walcott injury concern for Arsenal

Theo Walcott did not emerge for training with the rest of the Arsenal squad ahead of tomorrow's Champions League clash with Olympiakos.

The 22-year-old England striker suffered a knee injury during the latter stages of the Gunners' 3-0 win over Bolton last Saturday and, although it is not believed to be a serious problem, it was enough to stop him joining his team-mates at the start of their training session this morning.

Despite missing at least some of the session Walcott could still feature against Olympiakos as Arsenal look to follow up a 1-1 draw against Borussia Dortmund with their first win of this season's group stages.

Centre-back Laurent Koscielny (ankle) and forward Gervinho (hamstring) will certainly miss tomorrow night's clash against the Emirates Stadium.

Midfielder Yossi Benayoun (thigh) and centre-back Johan Djourou (hamstring) remain out.

Midfielders Jack Wilshere, Abou Diaby and defender Thomas Vermaelen continue their rehabilitation from ankle injuries.

Provisional squad: Szczesny, Sagna, Mertesacker, Song, Gibbs, Rosicky, Arteta, Ramsey, Frimpong, Arshavin, Van Persie, Fabianski, Chamakh, Coquelin, Oxlade-Chamberlain, Santos, Jenkinson, Miquel, Miyaichi.