Everton boss Rafa Benitez admits Dominic Calvert-Lewin is facing five weeks out.
The England striker has only played three Premier League games this season due to a quadriceps injury sustained after scoring in the 2-0 win at Brighton at the end of August.
He was due to return soon but aggravated the problem during training this week and is now not set to be back in the side until the end of November.
"Dominic has a re-injury," Benitez told a press conference ahead of Everton's game at home to Watford on Saturday.
"How long he will be out, it depends on how he reacts to the treatment. We will not see him for four or five weeks, could be, and we'll see later on what is going on.
"It's important to see how the player is improving and how he feels."