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.