Manchester United boss Ralf Rangnick admits Fred suffered a hip flexor injury in defeat at Everton.
Paul Pogba came on to replace the in-form midfielder after 36 minutes, with United a goal down, and Fred was visibly disappointed as he left the field at Goodison Park.
United were already missing Scott McTominay, who had to sit out of the trip to Merseyside having suffered a foot issue.
After the match, Rangnick told MUTV: “It seems to be some muscular issue on his hip flexor, probably, I don't know exactly what it is, but from the way that he explained it to me it seems to be a muscular problem.
“After Scott McTominay, missing a second defensive midfielder, let's hope that they will not be out for too long."
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