Eidur Gudjohnsen has been ruled out for up to four months after he broke his leg for AEK Athens against Olympiakos.
The striker, who was taken off after 46 minutes, was confirmed to have broken his fibula.
AEK's 1-1 draw with their rivals has kept them top of the league on goal difference.
The former Chelsea and Barcelona forward signed a two-year-deal with the Greek club over the summer.