Yerry Mina could be out for a number of weeks after suffering a tear in his left thigh.
The Colombian’s injury is a blow to Everton, coming less than a fortnight before the resumption of the Premier League season.
The centre-half has established himself as a regular under Carlo Ancelotti this campaign.
Mina will join Jean-Philippe Gbamin on the treatment table after suffering the partial quad tear in training last week.
A short statement on Everton’s website said:
“Everton Football Club can confirm Yerry Mina is set to be sidelined for several weeks after sustaining a muscle injury.
“The 25-year-old is now in the early stages of his rehabilitation under the care of the club’s medical staff and is making good progress.”
Gbamin, meanwhile, only played twice for Everton following his £25m move from Mainz last summer before being stricken by his own quad problem which required surgery.
The 24-year-old will undergo a second surgery later this week and the club expects the Ivory Coast international to require an “extensive period of rehabilitation”.