Arsenal are still assessing the severity of record signing Mesut Ozil's hamstring injury.
The Germany international - a £42million buy from Real Madrid last summer - suffered the problem during Tuesday's 1-1 last-16 draw at Bayern Munich which saw Arsenal exit the Champions League.
Speaking ahead of Sunday's north London derby with Tottenham, Arsene Wenger told arsenal.com: "He's out. I don't know for how long but it is a hamstring injury. There are scans going on."
In a further blow, given Jack Wilshere's absence with a broken foot, midfielder Aaron Ramsey's return from a thigh injury has been delayed.
Wenger added: "We have had to defer his comeback to full training so he is not available. He is having difficulties in the final stages of his rehab. It looks to be short term."
Left-backs Kieran Gibbs and Nacho Monreal have a "good chance" of being available. Gibbs has a fitness test on Friday.
Swedish midfielder Kim Kallstrom could be in contention for his debut after signing despite a back injury, while Yaya Sanogo is available.
Wenger said: "Kallstrom joins the normal training group today and Sanogo too.
"I will have to decide if Kallstrom is okay to be in the squad on Sunday. I will see how he looks. It is not impossible."
Meanwhile Arsenal striker Nicklas Bentdner faces a dressing-down from manager Arsene Wenger and a club fine for an alleged drunken incident in Copenhagen earlier this week, according to PA.
The 26-year-old is reported to have threatened a taxi driver during an incident in the Danish capital on the evening Arsenal exited the Champions League to Bayern Munich in Germany.
Wenger is understood to be aware of the incident, in which it is claimed Bendtner unbuttoned his trousers and rubbed against the taxi, and will speak to the striker.
Bendtner has not played for the Gunners since February 2, but did start for Denmark in the Wembley friendly against England last week.
He spent spells on loan at Sunderland and Juventus in recent seasons and is poised to leave Arsenal when his contract expires at the end of the campaign.