Di Maria was a notable absentee as United extended their unbeaten run in the Premier League to eight matches thanks to a 3-1 win over Newcastle at Old Trafford on Friday.
The Argentina international midfielder was expected to feature against Newcastle after recovering from a hamstring injury that allowed him to play a role at Villa Park last week.
But United manager Louis van Gaal revealed Di Maria sustained an injury in training and the club is now waiting to find out the significance of the problem.
"In the last training session, he [Di Maria] stepped out of the warming up," Van Gaal told reporters following Friday's win.
"It was a little bit amazing because he did everything very well, but he stepped out and now we have to wait and see for the analysis."
Di Maria has scored three goals in 11 Premier League games since joining United from UEFA Champions League winners Real Madrid in a British record fee of £59.7 million.
