Chelsea manager Enzo Maresca has confirmed forward Nicolas Jackson has been ruled out for "around six to eight weeks" with a hamstring injury.
The 23-year-old came off injured against West Ham two weeks ago and, although Maresca was initially hopeful the Senegal striker had avoided a major setback, scans have since revealed the problem to be worse than feared.
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 Jackson at West Ham, picked up a serious groin injury in the same match.