Mourinho tried to sign Pogba for Chelsea last season
Chelsea's move for Pogba was blocked by an agreement between the player's agent and Juventus, Mino Raiola said on Thursday.
Pogba, who left United for free to join Juventus in 2012 at the age of 18, returned to Old Trafford in a world record 105m euro deal earlier this summer.
Chelsea "really wanted" Pogba
But Raiola told Rai Sport: "Paul could have left (Juventus) last year because (Jose) Mourinho - then at Chelsea - really wanted him.
"But Juventus and I had agreement: win the league title and the Champions League, then he can go."
Juventus claimed a record-equalling fifth consecutive Serie A title last season but their progress in the Champions League was ended at the quarter-finals stage by Bayern Munich.
Napoli "should give Paul a present"
Raiola, meanwhile, said Pogba can expect a present from Napoli president Aurelio De Laurentiis because his transfer to United prepared the way for Juve to buy striker Gonzalo Higuain from Napoli for 90m euros.
He added: "De Laurentiis should be giving Paul a present, because without his departure Juventus would never have bought Higuain, and he would never have been able to bank all that money."