The 23-year-old Frenchman departed Old Trafford for Juventus in 2012 and has since grown into one of the finest midfielders in world football.
During the coverage of the Euro2016 final on Sunday night, former United star Ferdinand spoke of his old Red Devils colleague who he feels was let go too easily by Ferguson despite everyone else at the club knowing he was a star in the making.
"This is potentially the £100m kid at 23 years old, he's got huge potential," Ferdinand said on the BBC1's coverage of France's eventual 1-0 defeat to Portugal in Paris.
"The thing that stood out for me when I first met him other than he ability was his personality.
"This kid wants to be the best, he started this tournament very anxious, like a kid who had something to prove after he'd been hyped up and was worthy of that hype but he's grown into this tournament [for France].
"Didier Deschamps has got to take credit as he's put him in a deeper role and we've seen what tools he's got in the bag, from his range of passing, playing through the lines into the centre forward, he looks more composed and has more time in that position.
"He's really grown in stature in the tournament and they rely on him in many areas.
"He's the poster boy of this tournament, there's a lot of pressure on his shoulders and he's got a fantastic future."
He added: "His star quality was undoubted.
"There was not one person in that changing room who wasn't sure. Everyone in that changing room knew that him leaving was a huge, huge error."