Keane, alongside his brother Will Keane, was part of the Man United team that won the FA Youth Cup in 2011.
Pogba, Jesse Lingard and Ravel Morrison also represented the Red Devils during that triumph, and Keane has claimed that he did not expect the French midfielder to return to Old Trafford after leaving for Juventus in 2012.
"It's a little surprising to see him back at United, but I'm not surprised that they were willing to spend that kind of money," Keane told Goal.com. "The superstar image that he has got adds to his value and you could tell he was going to have that from a young age."
Pogba completed a return to Man United after helping France reach the final of Euro 2016.