Arouna Koné is set to have an operation on a knee cartilage problem which could rule him out of the rest of the season.
The Ivory Coast international was injured in the 2-1 win over Hull on 19 October and last week manager Roberto MartÃnez revealed it was more serious than first thought.
Everton have confirmed Koné, who turns 30 next week, will need surgery and the club believe it will significantly impact the part the forward plays in the rest of the season.
“We had disappointing news (in that Koné) will need a bit of a period away,” Martinez told evertontv. “We need to give him a lot of support because he was enjoying his role when he came on against Hull and then he got a nasty incident that is going to keep him away for a long time.
“He had a loosened body, a bit of cartilage in his knee, so we need to repair that which will take time.
“We´re going to work on other aspects of his body to get him fully fit and strong so that when he comes back, he is ready to enjoy his football.
“It´s going to be a long spell out and that´s disappointing.