United finally brought in a midfield reinforcement when they signed Amrabat from Fiorentina on an £8 million ($9.9m) loan.
However, it appears that the Moroccan is already injured and has had to withdraw from international duty.
United detected a minor back issue during Amrabat’s medical at Carrington.
He was, however, still released to join up with the Morocco squad.
It now seems that the issue was slightly more serious than first thought.
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United boss, Erik ten Hag, will be hoping that Sofyan Amrabat does not add to the growing injury crisis at Old Trafford.
If the midfielder recovers in time, he could make his United debut at home to Brighton on September 16.