Everton's attacking midfielder Iliman Ndiaye has sustained a medial ligament injury that is "not looking great," manager David Moyes said on Friday.
The 24-year-old Senegal international limped off in tears after picking up the knee injury during the first half of the Merseyside derby against Premier League leaders Liverpool, which ended in a 2-2 draw at Goodison Park on Wednesday.
Ndiaye, who is Everton's leading goal-scorer in the Premier League this season having netted six times, hurt his knee after accidentally hitting the ground with his foot while trying to kick the ball.
"He's got a medial ligament injury. It's not looking great. Not sure how long it'll be -- it will certainly be a few weeks," Moyes told reporters.
Everton, who are 15th in the league with 27 points from 24 matches, visit 12th-placed Crystal Palace on Saturday.