Arsenal will be without Theo Walcott for up to a month because of a medial knee ligament injury.
Walcott, making his first start of the season, had to be taken off during the first half of Saturday's 3-1 win over Birmingham following a challenge from Liam Ridgewell.
"The news is not good. We are without Theo Walcott for longer than expected," said Arsenal boss Arsene Wenger ahead of Tuesday's Champions League meeting with AZ Alkmaar.
"We thought it would be just 48 hours but it is a medial knee ligament, which is what I feared after the game. He will be out for three to four weeks."
Czech midfielder Tomas Rosicky (knee) is also unavailable for the AZ match, but full-back Gael Clichy has shaken off an ankle problem which kept him out of the Barclays Premier League win over Birmingham.
Samir Nasri, who broke his leg during pre-season, and goalkeeper Lukasz Fabianski (knee) will continue their rehabilitation with the reserves on Tuesday night, but strikers Nicklas Bendtner (groin) and Eduardo (groin), midfielder Denilson (back) and centre-half Johan Djourou (knee) remain sidelined.
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