Chelsea forward Nicolas Jackson, who has scored nine goals and provided five assists in al competitions this season, has been ruled out for around six weeks with a hamstring injury.
The 23-year-old came off injured against West Ham two weeks ago and, although manager Enzo Maresca was initially hopeful the Senegal striker had avoided a major setback, scans have since revealed the problem to be much worse.
Jackson has scored nine goals so far this season, making him Chelsea's second-top goalscorer behind Cole Palmer with 14.
It leaves the Blues without a recognised number nine after Spaniard Marc Guiu, who replaced the injured Jackson at West Ham, picked up a serious groin injury in the same match.
Maresca had initially said it was "not a big injury" for Jackson, but 19-year-old Guiu would be out for "weeks or months".
Palmer and Christopher Nkunku are likely to deputise in the duo's absence, with the latter starting in the 2-1 FA Cup fourth-round defeat by Brighton last Saturday.
Maresca's side, who are fourth in the Premier League, visit Brighton again in the league on Friday.