Powell picked up the injury during Man United’s U21s game against Everton earlier this month and had to be taken off before half-time.
It was hoped the 20-year-old would recover quickly but reports from Ian Ladyman suggest the injury has now been found to be relatively severe and that Powell faces a number of weeks on the sidelines.
It is the latest in a series of disappointing blows for the Englishman, who was brought to United from Crewe Alexandra for £4m in the summer of 2012.
Powell was highly-rated when the club signed him but the midfielder has struggled at United and has made only two substitute appearances in the Premier League.
He spent time on loan at Wigan Athletic and Leicester City but never really made a big impact despite impressing in spells.
Louis van Gaal recalled Powell to United from Leicester on the recommendation of assistant Ryan Giggs but his injury has delayed any chance of a first-team appearance.