Chelsea will be without Hakim Ziyech for the Boxing Day clash against Arsenal.
Blues head coach Frank Lampard confirmed the injury blow during his pre-match press conference on Wednesday afternoon as he may have to devise a plan without his chief creator.
Ziyech, who has enjoyed an impressive start to life in west London following his £33.4m summer transfer from Ajax, has missed the last four games in a row across all competitions.
This is after sustaining a hamstring injury during the first-half of Chelsea's win over Leeds United at the beginning of the month.
He did return to training ahead of the 3-0 win over West Ham United, but wasn't risked on Monday night.
And he won't be available for the weekend's trip to the Emirates Stadium.
"No, he won't be fit for Arsenal," Lampard revealed in his pre-match press conference. "It's a muscle injury so we need to wait for it to recover.
"Not a long-term concern and we hope to have him back in a week or so.
"That's football when players are playing every two or three days."
Meanwhile, Ben Chilwell and Reece James remain doubtful for the game against the Gunners.
James missed the 3-0 win over West Ham United with a knee injury and was replaced in the starting XI by club captain Cesar Azpilicueta.
Chilwell came off early with a twisted right ankle and had a scan on Tuesday to determine the extent of his injury.
However, Lampard has insisted that he can't confirm or deny either player will feature at the Emirates Stadium.
Furthermore, the Blues boss discussed whether the England duo could be fit for the clash against Aston Villa at Stamford Bridge 48 hours after the London derby.
"They are both doubtful. Can't give an answer.
"Not sure if fit for either game."
