Eric Bailly was withdrawn five minutes into the second half of the final pre-season friendly with Bayern Munich, while Ander Herrera appeared to feel his hamstring in the closing stages of the 1-0 defeat.
The Ivory Coast international had been a tower of strength up to that point but collided awkwardly with Serge Gnabry when making a robust challenge outside the United box.
Jose Mourinho wasted little time making a replacement, with Chris Smalling coming off the bench for his fellow centre-back and the boss told MUTV in an exclusive interview afterwards:
“For the ones who played lots of minutes, it was hard once more and Ander, we don't know, but it's between him and Eric, apart from that, the boys resisted and tomorrow, for them, is a day off.”
Herrera headed straight down the tunnel, apparently in some discomfort, with United allowed to bring on an extra substitute in 17-year-old James Garner, with Jose checking with his opposite number Niko Kovac that this was allowed.
Bailly was set to miss the match with Liverpool on Tour 2018 presented by Aon but entered the fray when Smalling was injured in the warm-up. Jose reported the defender had a swollen ankle afterwards but he has soldiered on in pre-season.
An update on the pair is likely to be provided in advance of Friday's Premier League opener against Leicester City at Old Trafford.
United lost the final pre-season friendly to Javi Martinez's goal at the Allianz Arena.
Reds beaten in Bavaria Gallery
The best images from the Reds' final pre-season outing at the Allianz Arena.