Rasmus Højlund, however, looks like one who might have a future at Old Trafford under new head coach Ruben Amorim. The Denmark striker came on midway through the second half at Doosan Arena, and a UEFA Europa League tie that looked like it might end in an embarrassing defeat was won by the finest of margins.
Højlund scored twice, including an 88th-minute winner, to help United record a scrappy 2-1 win that moves them up into the top eight of the table. In that respect, it was job done for Amorim's team, but the Portuguese boss will have seen plenty to worry him ahead of the trip to Manchester City on Sunday.
André Onana's form is a particular concern after his error gifted Viktoria Plzeň the lead just days after the goalkeeper was at fault for two goals during Nottingham's Forest's 3-2 win at Old Trafford on Saturday.
Onana looked like a relieved man when Højlund scored late on, running the length of the pitch to join the celebrations. Relief was the overriding emotion for his manager, too, after a largely frustrating night.
"It was not a great game but we managed to do these good things and I think we deserved the win," Amorim said afterward. "You want to see better things but then you remember that we didn't have so much time to work.
"I think clearly we had a lack of pace during the first half. I'm always frustrated. I think I'm going to be like that for a while."
Højlund ensured a freezing night in Czechia ended on a high note as United earned their first away win in Europe since March 2023, but the first half was one of the worst under Amorim so far. United weren't helped by a bobbly pitch, although even that wasn't an excuse for some of the misplaced passes during a turgid first hour.
Amorim said on his first day in the job that his team gives the ball away too much. It has been a month, and he's still trying to fix the issue. The sloppiness was summed up by Joshua Zirkzee.