Christian Pulisic will be out for "weeks" with a knee injury, according to Chelsea manager Graham Potter.
The United States winger was forced off in the first half of Chelsea's 1-0 loss to Manchester City on Thursday in the Premier League after a challenge with John Stones.
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He missed the 4-0 defeat to Pep Guardiola's side in the FA Cup third round on Sunday, and Potter said after the match that Pulisic is set for a spell on the sideline.
"Christian opened up his knee in the game the other day, so we're still analysing it, but it is going to be weeks," Potter said when asked about Pulisic's injury.
Potter is facing a growing injury list at Chelsea, who have lost six of their past nine games. Raheem Sterling also missed the cup tie at the Etihad Stadium after being substituted after five minutes against City at Stamford Bridge.
"Raheem had an action, first minute of the game, he felt something in his hamstring so, again, we are analysing it," Potter said.
Striker Pierre-Emerick Aubameyang was unable to travel to Manchester because of a back injury, while Chelsea are also without Reece James, N'Golo Kante, Ben Chilwell, Wesley Fofana, Edouard Mendy, Ruben Loftus-Cheek and Armando Broja.