Everton manager Roberto Martinez fears Romelu Lukaku could face a lengthy absence after the striker injured his ankle in Tuesday's derby defeat at Liverpool.
Lukaku collided with teammate Gareth Barry while defending Luis Suarez's corner, from which Steven Gerrard opened the scoring in a 4-0 win for Liverpool at Anfield.
The Belgium striker, who has scored nine goals so far for Everton this season, could face a lengthy absence, with Martinez admitting he is concerned and is waiting to discover the extent of the problem.
"We are going to assess it, he has his ankle in a cast but it does not look too good. He picked up a bad injury," Martinez told his postmatch news conference. "He just collided with Gareth Barry in the corner as the ball was delivered into the near post. There was a collision and he got an ankle twisted.
"There are moments in games that can be very painful, and that was one of them. Not only did we concede from a dead-ball situation, two of our players collided and Romelu got injured."
Everton remain in sixth in the Premier League table following the defeat, but Manchester United's 2-0 win over Cardiff saw them move within two points of the Toffees.