Jose Mourinho expects Juan Mata to join Phil Jones and Chris Smalling among Manchester United's long-term injury absentees as the team approach a crucial period in their challenge to qualify for the Champions League.
Spain international playmaker Mata underwent groin surgery last week, with no specific timescale given on his anticipated return to fitness.
Defenders Jones and Smalling suffered leg and toe injuries respectively while on international duty with England and are also not expected back in the near future.
United are at home to Everton in mid-week as they attempt to improve on a frustrating 0-0 draw against West Brom at Old Trafford, a result that has left them five points behind fourth-placed Manchester City in the race to qualify for UEFA's elite competition next term.
"I think a long time," Mourinho told a news conference when asked about the duration of Mata's probable unavailability.
"I think Mata, Jones and Smalling for a long time."
Of world-record signing Paul Pogba, who has been out with a hamstring strain, Mourinho added: "Pogba I cannot say is ready for Tuesday because I don't know but Pogba is not such a long-term injury as the others."
The Portuguese also denied suggestions that star striker Zlatan Ibrahimovic, who has missed the past two league matches through suspension, would have made the difference against West Brom.
"I don't know," he said.
"We had matches here with Zlatan that we drew. He lost a penalty in the game 2-1 [against Bournemouth], he lost chances like other people did too, so I cannot say now that if Zlatan and Mata played on Saturday we win the game, I cannot say that."