Everton's attacking midfielder Iliman Ndiaye (24) will be sidelined for at least a few weeks after sustaining a medial ligament injury, manager David Moyes (61) said on Friday.
The Senegal international limped off in tears after picking up the 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.