Arsenal manager Arsene Wenger has confirmed midfielder Francis Coquelin will be out for at least two months with knee ligament damage sustained in their 2-1 defeat at West Brom on Saturday.
Coquelin was forced off just 14 minutes into Arsenal's loss at the Hawthorns, their first in the Premier League since going down 2-0 at Chelsea in September.
The Frenchman suffered the damage while tackling West Brom midfielder Claudio Yacob and was replaced by Mikel Arteta.
Wenger said: "I'm always cautious. It will be at least two months but I don't want to speculate more than that."
Confirmation of the length of Coquelin's lay-off is another significant blow to an Arsenal side ravaged by injuries, having faced West Brom without Jack Wilshere, Danny Welbeck, Tomas Rosicky, Theo Walcott, Aaron Ramsey and Alex Oxlade-Chamberlain.
Wenger indicated he could dip into the transfer window in January to bolster his playing resources, but has contingency plans in place to cope with Coquelin's absence.
"I must say we have been hit very hard in November. We have lost a few players," he added.
"We have [Mathieu] Flamini who can play there, also [Calum] Chambers because he has been educated as a central midfielder.
"It depends now what comes out of the scan with Francis and we will see.
"I will do what is needed in Janaury, knowing as well that in January it is not an ideal transfer market."