Everton have confirmed that winger Yannick Bolasie will require surgery on what they describe as a "serious" injury to his knee.
The 27-year-old was substituted in the 68th minute of Sunday's 1-1 Premier League draw with Manchester United and was sent for scans on the problem.
The club have since announced that Bolasie has sustained cruciate ligament damage and will be operated on this week.
"Yannick Bolasie will undergo surgery after sustaining a serious knee ligament injury against Manchester United on Sunday," an Everton statement said.
"Scans have now confirmed anterior cruciate ligament damage to the right knee. Bolasie will undergo surgery in the next few days."
Initial reports have suggested that he could be out for the remainder of the season.
Bolasie has been ever-present in Ronald Koeman's side since arriving from Crystal Palace in August for a reported fee of £27million.
The DR Congo international has scored one goal and provided four assists in those 16 appearances in all competitions.