Ander Herrera was the first to go off. The Spanish midfielder had got off to a fine start, providing a beautiful cross to set up Memphis for United's opener on 11 minutes.
But Herrera limped off at the 25-minute mark clutching his hamstring and shaking his head.
Then, with just over 20 minutes to go, Phil Jones went down injured. At first, the England defender tried to continue, but he clearly decided he was unable to do so and came off.
Luiz floored Ceballos during fight at Arsenal training ground - report
His replacement was Paddy McNair - himself only just back after an abdominal injury suffered in September.
Louis van Gaal now has Herrera, Wayne Rooney, Anthony Martial, Michael Carrick, Marouane Fellaini, Antonio Valencia, Luke Shaw and Jones out.
United fans' hearts were in their mouths yet again as the match entered the final 10 minutes, with Ashley Young going down. With all three subs used, however, Young carried on playing, suggesting that the injury is at least not too serious.
Manchester United's Phil Jones
Image credit: Reuters
This injury is a particularly cruel blow for Jones: according to Physioroom.com statistics, it is the sixth injury he has sustained in 2015 alone, with a blood clot in his calf keeping him out of action for almost three months at the start of the season.
After coming back from that injury, Jones spoke about how hard it had been: "It was one of the most frustrating periods of my career, sitting at home not being able to do anything," he said.
"I don't think anyone will ever realise how hard it is at times. But I don't want any sympathy. I am just happy to be back."
Manchester United fans will be hoping that this latest blow will at least prove to be less serious than the last.
Havertz returns to Chelsea training after positive Covid-19 test
Newcastle United confirm legal dispute with Premier League over failed Saudi takeover