Jose Mourinho says midfielder Ander Herrera picked up a “bad injury” in their goalless draw with Sevilla in the first leg of their last-16 tie in Spain.
Herrera has struggled with a muscle problem in recent weeks but was passed fit to play at the Ramon Sanchez Pizjuan.
But the Spaniard was forced off after just 17 minutes against Sevilla with what appeared to be a hamstring injury.
“I think it is a bad injury,” said Mourinho.
“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.”
Herrera was playing his first game for United since the 2-0 defeat to Tottenham at Wembley on January 31.