Manchester United manager Jose Mourinho expects Luke Shaw to have a "big injury" after the defender had to be substituted in the draw with Swansea.
Shaw, who was criticised by Mourinho earlier this month, left the field after nine minutes with an injury to his left leg.
United, who meet Celta Vigo in the Europa League semi-finals on Thursday, also lost fellow defender Eric Bailly.
Marcos Rojo, Phil Jones and Chris Smalling are already sidelined.
"I think Luke Shaw's must be a big injury, because to leave the pitch after nine minutes, I am expecting a very big injury," said Mourinho.
"At the moment, we can walk from the bed to the toilet and break a leg."
Neither Jones [toe] nor Smalling [knee] have played for United since 19 March, but midfielder Juan Mata did return to the bench after it was thought he would be out for the remainder of the season following groin surgery.
"I prefer not to speak about Phil Jones and Chris Smalling," added former Chelsea boss Mourinho. "I prefer to speak about Juan Mata giving everything to be available. I am grateful for that."
United's fixtures 'not human'
As a result of their run to the Europa League semi-finals and the need for some Premier League games to be rearranged, United have played nine games in April, with the potential for another seven by 24 May.
"We are tired and exhausted," said Mourinho. "This is the ninth match of April, it is not human. We have a squad of 22 that is reduced to 13 or 14 players."
The 1-1 draw with Swansea left United fifth in the Premier League and a point off the top four with Champions League qualification also possible by winning the Europa League.
In a passionate explanation to reporters, Mourinho said that a potential Europa League final could be played in "disastrous" circumstances and that he may be forced to play his club's under-23 side against Crystal Palace on the last day of the Premier League season.
"Imagine if we were also in the FA Cup semi-final," he said. "We would have had a game against Burnley that would have to be played later.
"When? After the FA Cup final? In June? In next pre-season? In the end, it was a blessing that we didn't make the cup semis.
"You are punished because you are doing well. If we beat Celta, we have the final. The final is on the Wednesday after we have played Crystal Palace on the Sunday and Southampton the Wednesday before that.
"Maybe I can bring Nicky Butt and his under-23 team to play Palace. Hopefully they don't need the points to stay in the division, because it would be very bad if we play with the under-23s. It's difficult."