Everton boss Ronald Koeman has said Yannick Bolasie will be absent for between 10 and 12 months with his knee ligament injury.
Bolasie, 27, sustained the injury in the 1-1 draw with Manchester United last month and has undergone the first of two operations.
Koeman told the club's annual general meeting on Wednesday that the DR Congo international, who joined from Crystal Palace in the summer for a fee of around £25 million, will not return in time for the start of next season.
"He's optimistic," Koeman said. "It was difficult because it is a really long-term injury, he will be around 10, 11, 12 months and that is really disappointing.
"First for the player and then for the club and also the manager, because he was one of the good signings that the club made this summer, but, OK, he's still 27 years old, he will come back.
"He has a strong mentality and we are looking forward to when he is back on the pitch."