Abdoulaye Doucoure will be out for a lengthy spell with a foot problem in a further injury setback for Rafael Benitez but will not need surgery.
The midfielder has been key for Benitez this season, producing two goals and four assists in the league - a superior contribution to the entirety of the previous campaign in 21 games fewer - but will now only have a watching brief after sustaining the injury in Sunday's 1-0 home defeat to West Ham.
ℹ️ | Abdoulaye Doucoure sustained a stress response in his foot against West Ham but will not require an operation.— Everton (@Everton) October 19, 2021
Speedy recovery, Abdoulaye! 💙
Everton released a statement regarding the midfielder's injury on Tuesday, which read: "Everton can confirm that Abdoulaye Doucoure has suffered a stress response in his foot sustained during Sunday's match against West Ham United.
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"The French midfielder is being assessed by the club's medical team at USM Finch Farm and is undergoing further investigation to determine the full extent of the injury.
"Contrary to reports, Doucoure will not require an operation."
It could leave Everton light in midfield for Saturday's visit of Watford in the Premier League with Andre Gomes and Fabian Delph both recovering from injury.
Forward players Dominic Calvert-Lewin and Richarlison have also struggled with fitness this season and their involvement is in doubt for the forthcoming league match.
Benitez, who says Richarlison is further along in his recovery than Calvert-Lewin, admits that while Everton have coped well in the pair's absence, they were sorely missed in the 1-0 defeat to West Ham at the weekend.
"I think Richarlison is closer, Dominic will take longer but Richarlison is getting closer," Benitez said.
"The fact we were winning without Richarlison or Dominic means we could do it the same but when you play against a good team and you have some chances you have to take them and if not you have to carry on.
"Missing these players you have less chance to change and put fresh legs on.
"When you play against a good team it is more obvious it is a problem but still we were winning and we have to keep on winning."
Analysis: Doucoure loss is sizeable; enter Gbamin?
Sky Sports' Ben Grounds:
"Following a summer of austerity in the transfer market at Everton, there is a lingering fear among the fanbase that the club's growing injury list will derail a fine start to the season.
"Sunday's home defeat to West Ham was a sobering one, with Rafa Benitez's decision to make just the one substitute as his team searched for a rescue act symptomatic of the lack of squad depth exposed by the absence of key personnel.
"The Everton manager revealed afterwards that Richarlison is closer to a return than Dominic Calvert-Lewin, but no time scale has been placed on either forward.
"Yerry Mina was greatly missed in defence and the Colombian will return against Watford next weekend but Doucoure's absence will be the greatest felt in the coming weeks.
"An indication of what lies ahead came in the Carabao Cup penalty shootout loss at QPR, when Benitez sought to give the Frenchman a rest but ultimately was forced to introduce him in the second half in a vain attempt to win the game in normal time.
"The former Watford midfielder has been Everton's best player this season, and his importance extends far beyond his two goals and four assists.
"Indeed, no player in the Premier League has covered more ground than his 91.3km. Coupled with Everton's dramatic drop off in win percentage when he has not started games since his arrival in September 2020, and the outlook is bleak for the coming weeks.
"Doucoure missed several weeks towards the back end of last season with a fractured foot and Everton won just two of nine games in all competitions as their quest to qualify for European competition lost all momentum.
"Jean-Philippe Gbamin was named on the bench against West Ham. The Ivory Coast midfielder has played just four times in all competitions since joining the club in August 2019 due to his well-documented and persistent injury troubles.
"With Andre Gomes and Fabian Delph still out of the picture nursing their own injuries and Tom Davies unfancied under Benitez, this is an opportune moment for Gbamin to step forward to fill the sizeable Doucoure void."
Doucoure is now in a race against the clock to be fit for the Merseyside derby on December 1.
He will be sidelined for upcoming games against Watford, Wolves, Tottenham and Manchester City while he will almost certainly be missing for the trip to Brentford on November 28, live on Sky Sports.
A stress fracture tends to require six to seven weeks to recover from, which could mean him missing the visit of Liverpool to Goodison Park as well as the Arsenal encounter five days later.
October 23: Watford (h) - Premier League, kick-off 3pm
November 1: Wolves (a) - Premier League, kick-off 8pm, live on Sky Sports
November 7: Tottenham (h) - Premier League, kick-off 2pm
November 21: Manchester City (a) - Premier League, kick-off 2pm, live on Sky Sports
November 28: Brentford (a) - Premier League, kick-off 2pm, live on Sky Sports
December 1: Liverpool (h) - Premier League, kick-off 8.15pm
December 6: Arsenal (h) - Premier League, kick-off 8pm, live on Sky Sports