In his four years in Turin, he won four league titles and two cups. Massimiliano Allegri is the manager of the club and he will be working with him again.
According to sources, Pogba was interested in returning to Bianconeri after he turned down the chance to play for City.
The departure of Leonardo and the arrival of Luis Campos made Paris Saint-Germain less interested in signing the France international.
The documentary "The Pogmentary" will be released on Amazon Prime on Friday.
It was confirmed earlier this month that the player would leave when his contract expired.
The then world-record fee for a player was paid by Paul Pogba when he came back to United in 2016 after a spell in Italy.
He won three trophies in his first season, but fell out with his manager and struggled to find consistency under different managers.
In his last two appearances for the United fans, they booed him, despite the fact that he had an uneasy relationship with them.