Jose Mourinho has little hope of a speedy recovery for Ander Herrera, who lasted just 17 minutes into his Manchester United return against Sevilla on Wednesday.
Herrera had to be replaced by a benched Paul Pogba after pulling up in his first game since facing Tottenham at Wembley on January 31.
The 28-year-old Spanish midfielder, who was declared fully fit ahead of this game, pulled up with an apparent hamstring injury when attempting a backheel.
After the game, Mourinho said: “I think it is a bad injury.
“He had a small injury that stopped him for the last couple of matches but the medical team said he was 100 per cent ready for the last Saturday. It didn’t look like he was fully fit.
“We didn’t play him to give more work and more protection, but it looks like he was not fully fit.
“The medical department gave him fully fit. They gave him fully fit Saturday and he trained Saturday, Sunday, Monday, Tuesday, and he looked fit.
“The way he was playing during the time he was on the pitch, I think he showed that intensity that is only possible when you are fit.
“He was pressing really high, we start the match not giving one inch to (Ever) Banega, pressing him really high. Ander was one of them, Scott (McTominay) was the other one, and you only do that when you feel really good.
“Then the back-heel creates a contraction in the muscular area where he had a fitness problem, and now we have the proof that he was not 100 per cent fit.”