Everton full-back Lucas Digne will be sidelined for "two to three months" after suffering an ankle injury in training this week.
The France international, 27, is set to have surgery on Monday "before commencing his rehabilitation".
Manager Carlo Ancelotti said Digne was a "big loss because he is one of the best left-backs in Europe".
The defender has been one of the outstanding performers this season for Everton, who are sixth in the league.
Niels Nkounkou, 20, who joined Everton on a free transfer from Marseille in July, is likely to deputise for Digne.
Digne's absence is a major setback for the Toffees, who host Chelsea, Arsenal and Manchester City in the Premier League in December as well as having a trip to Leicester City and a Carabao Cup quarter-final at home to Manchester United.