Jose Mourinho said he was not feeling optimistic about the injuries sustained by Zlatan Ibrahimovic and Marcos Rojo as Manchester United secured a place in the Europa League semi-finals.
Thursday's quarter-final second leg against Anderlecht at Old Trafford, which United won 2-1 in extra time on the night for a 3-2 triumph on aggregate, saw striker Ibrahimovic hobble off after landing awkwardly towards the end of normal time and defender Rojo depart on a stretcher in the first half.
Asked about the condition of the pair, Mourinho said: "I want to wait, but my feeling is not good for both.
"I want to wait and try to be optimistic, but I am not."
Rojo's injury comes at a time when United already have Phil Jones (foot) and Chris Smalling (knee) sidelined.
When it was put to him that he was facing a significant lack of options at centre-back, Mourinho mentioned Daley Blind - Rojo's replacement from the bench - before suggesting Jones and Smalling needed to be "brave".
Mourinho, who earlier this season made an apparent criticism of Smalling's pain threshold, said: "We have Daley Blind, who has experience in the position, and I think it is time for Jones and Smalling to be brave - to risk.
"Because for the team you have to do everything, that is the way I think. You cannot do miracles, so miracles I don't expect, but they have to try to do everything to accelerate the process.
"They have injuries, and even with a crazy mentality, they cannot play Sunday (at Burnley in the Premier League).
"But with a special spirit, you can (come back) sooner than expected. So instead of mid-May, it could be the beginning of May, this kind of acceleration of the process."
Mourinho also emphasised the trust he has in Marcus Rashford, whose fine 107th-minute strike settled the tie.
It had gone to extra-time thanks to Sofiane Hanni's effort around the half-hour mark for the impressive visitors, which cancelled out Henrikh Mkhitaryan's 10th-minute opener.
Regarding 19-year-old Rashford, Mourinho said: "It is hard for the kid to play every match, but I always trust the players with special mentalities.
"That is why I kept Marcus on the team the whole time - for months he was not scoring a goal, but my trust in the boy is always based on his mentality.
"In spite of being a young kid, other guys can look at him. We have great examples of fighters, of people with the right mentality."
Ahead of Friday's draw for the semi-final, which also features Ajax, Lyon and Celta Vigo, the Portuguese added: "I'm relieved. I'm happy.
"It was a difficult game, difficult opponent.
"I am tired. I imagine the players are more tired than me. But we are in the draw for tomorrow and we still have the dream to win the competition."