Chelsea manager Frank Lampard says midfielder Billy Gilmour will be out for about three to four months after having a knee operation.
The 19-year-old Scot has moved up to training permanently with the Blues' first-team this season and has made 11 appearances during the campaign.
"I'm very disappointed, as we all are here," said Lampard.
"He's a tough boy, it hit him hard especially as a young boy who has just made a breakthrough."
Gilmour, who joined Chelsea from Rangers in 2017, put in a particularly impressive performance when he helped the Stamford Bridge club beat Liverpool in the FA Cup fifth round in March.
"I told him he should be very pleased with what he's done and the impact he's had this season anyway," added Lampard.
"His attitude will get him back as quickly as he can."