The ex-Jambo picked up the injury against Auchinleck Talbot in February. He suffered a reoccurrence of a knee problem that forced him to miss part of the 2017/18 campaign.
Now Mitchell, who made his senior Red Devils debut in the 2016/17 season, is training on the grass again.
What does the future hold for the ex-Gorgie man though?
Mitchell won’t be at Manchester United for long
Mitchell really impressed on his first Tynecastle loan stint, prompting Craig Levein to bring him back for a second spell. Things just weren’t the same though.
He seemed to think he was playing at left midfield. Mitchell would burst forward all the same, but would often be a liability going back the way.
Overall he made 23 appearances in what was challenging campaign for him.
Where does all of this leave his Red Devils career? The left-back’s Hearts form certainly suggested that he was struggling at Scottish Premiership level, never mind playing at one of the world’s biggest clubs.
Left-back is a problem position for the Old Trafford side though. With Luke Shaw injured, Ashley Young has been used in the full-back slot.
Whilst Young isn’t as good as he once was, the 34-year-old is capable of offering more than Mitchell, based on the latter’s Tynecastle experience.
Hearts’ former full-back may be returning to fitness, but don’t expect to see him in a Red Devils shirt in the near future.