Arsenal fear Olivier Giroud could be sidelined for up to four months after breaking a bone in his foot, Goal has learned.
Initial scans of the Frenchman's ankle suggested he could be out of action for around 10 weeks, but the Gunners are now facing the prospect of being without the former Montpellier man until the end of December.
"Giroud won't play tomorrow," admitted Wenger, who refused to put a timeframe on Giroud's return. "We'll make an announcement after the [Besiktas] game. We don't know if it's long term."
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Should Giroud be sidelined for four months it will be a huge blow for Wenger, who is also sweating over the fitness of Alexis Sanchez for the make-or-break Champions League qualifier against Besiktas.
The Chilean is carrying a knock sustained in the 2-2 draw at Everton on Saturday, although he is expected to pull through for the second-leg clash at the Emirates Stadium.
However, Giroud is preparing for a lengthy absence, which could force Wenger to make a late addition to his strike force in the final days of the transfer window.
An initial scan had failed to clear up the extent of the damage to an ankle injury suffered by Giroud during the closing stages of Arsenal's draw at Goodison Park and he was sent for a second examination after the inflammation of the joint had subsided, which revealed a broken bone in his foot.
In attack, Wenger now has only Sanchez, who led the forward line in the first half against against Everton before going off injured, unproven pair Yaya Sanogo and Joel Campbell, and Lukas Podolski.
The German had been told he could leave the club this summer, but Wenger has been forced into a U-turn regarding the World Cup winner's future following Giroud's injury and confirmed on Tuesday that he would not be sold.
He is likely to dip into the market for a new forward but his plans will depend upon whether Arsenal can overcome Besiktas on Wednesday night and progress into the lucrative Champions League group stages.
Arsenal's bid to recruit a new centre-back suffered a blow on Tuesday after they lost out to Roma in the race to sign Greece international Kostas Manolas.
He was undergoing a medical at the Serie A club on Tuesday after they trumped the Gunners by offering £10.3 million for the defender.