Arsenal manager Arsene Wenger fears Spanish midfielder Mikel Arteta will be sidelined for at least three weeks with a calf strain.
Arteta missed Sunday's 2-0 home defeat against Manchester City after suffering the injury in training earlier in the week.
The 30-year-old will have a scan on Monday to determine the full extent of the problem, but Wenger doesn't expect to have the former Everton star back before February.
"Arteta will have a scan on Monday, he has a strain on his calf," Wenger said. "It will be approximately three weeks. It is a blow because in midfield he gives us experience, stability and tactical knowledge. We will miss that."
Wenger acknowledged Arteta's injury would add to the pressure to bring in new players before the transfer window closes at the end of the month, but he remains determined not to panic buy inferior talent.
"We are in the market, but to find players of the calibre of Arteta in January, I wish you good luck," he added. "We try very hard, believe me. I don't want to talk specifically about names."