Arsenal centre-back Shkodran Mustafi will be out for at least three weeks after injuring a hamstring during his side's 3-1 win over Stoke.
The German, 24, was forced off after 25 minutes at Emirates Stadium.
"It's a bad one. The minimum is 21 days," said Gunners boss Arsene Wenger of Mustafi's expected absence.
Arsenal have three games in that period, facing Everton away on Tuesday, Manchester City away on 18 December, and hosting West Brom on 26 December.
Mustafi joined Arsenal from Valencia in August for a fee in excess of £32m.
The victory over Stoke took Wenger's men top of the Premier League on goals scored over Chelsea, who face West Brom on Sunday at 12:00 GMT.
Charlie Adam's penalty gave the visitors the lead before Theo Walcott, Mesut Ozil and substitute Alex Iwobi made it 12 goals in three games for Arsenal.