Italian full-back Matteo Darmian, who started at left-back at the Volkswagen Arena, was replaced by youngster Cameron Borthwick-Jackson just before half-time as the Red Devils slumped to a 3-2 defeat in the Champions League.
Central defender Chris Smalling got through the 90 minutes but was limping towards the end of the contest and has reportedly injured his groin.
After the match, Louis van Gaal revealed that Darmian had sustained a hamstring injury and confirmed Smalling's problem while suggesting the pair may be sidelined for the weekend's trip to Bournemouth.
Man Utd's Twitter page relayed the news:
Louis van Gaal says Darmian has a hamstring injury & Smalling probably a groin problem, with both doubtful to face Bournemouth on Saturday.
— Manchester United (@ManUtd) December 8, 2015
Luke Shaw is already sidelined with a badly broken leg and is not due back until well into the New Year, Antonio Valencia is out of action until February, Marcos Rojo is still out with a shoulder problem and Phil Jones remains on the outer but could return before Christmas as United continue to experience a major shortage at the back.