Everton midfielder Abdoulaye Doucoure has sustained a foot injury but will not require surgery, the club has said.
The Frenchman, 28, suffered a "stress response in a bone in his foot" during Sunday's 1-0 home loss to West Ham in the Premier League.
Everton's medical team is currently assessing the extent of the injury.
Rafael Benitez's side are already without injured midfielders Andre Gomes and Fabian Delph, plus forwards Dominic Calvert-Lewin and Richarlison.
Doucoure, who was out injured for several weeks earlier this year with a small fracture in his foot, has been in excellent form for the Toffees this season and has supplied the joint-second most assists in the Premier League.
Everton are due to host Watford in the league on Saturday at 15:00 BST.
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