Jean-Philippe Gbamin will be out of action for at least eight weeks after suffering a tendon injury in his right leg.
The £25million summer signing will miss a minimum of seven games for Everton with the first coming against Lincoln City in the League Cup on Wednesday night.
The Blues say they will establish a "full timescale" for the midfielder's right quadriceps injury in the coming weeks pending further investigations.
A statement on the club's website read: "Everton Football Club can confirm that Jean-Philippe Gbamin has sustained a tendon injury in his right quadriceps muscle, which will keep the midfielder out of action for at least eight weeks.
"The full timescale for the injury will be established following further investigations this week.
"The club are in communication with leading experts around Europe to ensure the optimal outcome."
