Abdoulaye Doucoure faces an extended period on the sidelines after damaging his foot in the defeat to West Ham.
The Everton midfielder is believed to have hurt a metatarsal and is looking at a prolonged spell out of the team, in a blow to Rafa Benitez.
Doucoure has been one of the Blues' most influential players this season and has responded to Benitez moving him into a more advanced position, with two goals and four assists in eight Premier League games.
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But Everton are now braced to be without the 28-year-old for, what could be, several weeks.
The ECHO initially reported that an operation was being lined up but Everton have said that he will not need to go under the knife.
Doucoure missed seven games last season with a foot fracture but the early indications are that the £20m man may be out for longer with this fresh injury.
Everton's medical department will continue to assess the player.
Everton's central midfield options are currently limited with both Andre Gomes and Fabian Delph also injured.
Doucoure's absence for the weekend's game with Watford is likely to mean a recall for either Tom Davies or Jean-Philippe Gbamin.
