Jonny Evans and Rafael da Silva have not travelled with the squad for Tuesday's game against Real Sociedad due to injury.
David Moyes confirmed that both players will be unavailable for the Champions League tie following injuries sustained in the 3-1 Premier League win over Fulham on Saturday.
Manchester United have, however, been boosted by the news that Tom Cleverly has recovered from the double vision that forced him off at half-time at Craven Cottage, and travels to the Basque region of Spain.
"We haven't had a lot of injuries - I think it’s the best Manchester United have been in that respect for a while," Moyes told reporters.
"But we did pick up three on Saturday, which is very rare - especially by half-time.
"Two of them haven’t travelled, Jonny Evans and Rafael, so they're not with us."
Manchester United sit comfortably atop Group A with seven points from their opening three games and have already beaten Sociedad 1-0 in the reverse fixture.
One more win will give the Red Devils the 10 point marker widely considered to be good enough to qualify.
With Sociedad having lost all three games so far, United are favourite for the win but Moyes is taking nothing for granted.
He continued: "I feel we're playing better and getting some good results to go with it.
"Long may that continue.
"I have a lot of respect for Sociedad. We have to play well if we’re going to get those 10 points, which will get us over the line.
"We've got ourselves into a good position in the group and we have to try to maintain that."