Jose Mourinho is concerned at the worsening state of Manchester United's injury crisis amid growing concerns that Zlatan Ibrahimovic and Marcus Rojo will not play again this year.
Thursday's progress to the Europa League semi-finals came at a cost as both Ibrahimovic and Marcos Rojo suffered knee injuries during the 2-1 extra-time win over Anderlecht.
Ibrahimovic, the 35-year-old striker who has scored 28 goals in all competitions in his debut competition in English football, suffered his injury when his knee buckled in an awkward fall.
Rojo had left the pitch on a stretcher earlier in the match against the Belgianss.
A statement from the club on Saturday said: "Detailed investigations on the injuries sustained by Marcos Rojo and Zlatan Ibrahimovic during Thursday's Europa League match have confirmed significant knee ligament damage in both players that requires specialist opinions over the coming days.
"Estimations of time to full recovery will only be possible once definitive treatment plans have been decided after these consultations."
Ibrahimovic's one-year contract is up at the end of the season, meaning it is possible the Swede has played his last game for the club, with speculation linking him with a move to Major League Soccer.
His loss is a blow to United's hopes of European success and their chances of securing a top-four finish in the Premier League.
At times he has carried the team this season, his form earning him a PFA Player of the Year nomination.
However, it is the loss of Rojo which is proving of greater immediate concern to United boss Jose Mourinho, who is having to cope with a debilitating injury list.
While the Portuguese is confident he has "options" up front, with Wayne Rooney ready to return, on the defensive front he is already without long-term absentees Phil Jones and Chris Smalling.
"We are in trouble," Mourinho said after Thursday's game.
"In this moment, Eric Bailly played six matches in a row, and we lost Marcos Rojo, we don't have Jones or Smalling, we are in trouble and now we lose Zlatan too.
"But in attack, we have options and (Wayne) Rooney is coming, and let's see if Mata can also return before the end of the season, let's see what happens."
The onus will be on Marcus Rashford and Anthony Martial to step up in Ibrahimovic's absence.
Rooney is another attacking option after returning to the bench against Anderlecht following ankle issues, with Mourinho backing his captain to have a big influence in the closing weeks of the campaign.
"He is a strong man, even if he is not in the best condition."
"He has a good mentality, he is a fighter," the United boss said ahead of Sunday's trip to Burnley, where he confirmed Ander Herrera would return to the starting line-up.
"He is a strong man, even if he is not in the best condition, even if he is not in the level of sharpness that you need to play high-level football, but he has the experience and character, so he has to.
"Now we need absolutely everyone, now I even have to think that Axel Tuanzebe, has to go to the under-something World Cup in Korea, because maybe Axel has to come now, now we need everyone."
