The tie was eventually settled in extra-time by man-of-the-match Marcus Rashford as a breathless quarter-final second leg ended 2-1 at Old Trafford, seeing Mourinho's men through 3-2 on aggregate.

But victory came at a cost as increasingly important defender Rojo left the field on a stretcher in the first half, before top scorer Ibrahimovic's knee buckled after landing awkwardly just before extra-time.

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."

Ibrahimovic was able to hobble off after the injury and Rojo told reporters he was "okay" while limping heavily through the post-match mixed zone.

The Argentina international, so impressive this term, is another blow to a defence already without Phil Jones and Chris Smalling.

Mourinho last week said the England centre-backs were out until mid-May, but suggested after the Anderlecht win that they need to be "brave".

"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," the United boss, who seemed to criticise Smalling's pain threshold earlier in the season, said.

"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 match-winner Rashford, whose turn and finish was impressive in such a high-pressure situation.

"It is hard for the kid to play every match, but I always trust the players with special mentalities," the United boss said.

"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."

United find out their semi-final opponents in Friday's draw, with Ajax, Celta Vigo or Lyon lying in wait.

"I'm relieved," Mourinho added. "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 and we still have the dream to win the competition."