United insisted on Monday night that Pogba is not for sale and they are believed to have rejected an opening offer from Barcelona of £44.6million plus two players - Yerry Mina and Andre Gomes.
In an interview with ESPN FC two weeks ago, Mourinho questioned why Pogba's performances in Russian Federation were so much better than his displays for United last season.
Pogba is now tempted to leave United for Barça - and it now seems clear that Mourinho is one of the main reasons why.
The Red Devils paid a then world-record €105 million to bring him back to the club.
"By building the team around him, Jose would be challenging Pogba to prove he is an elite player by delivering captain's performances every week".
Pogba's agent, Mino Raiola, is now in Manchester in a bid to push the complicated operation forward.
Pogba endured a turbulent time at Old Trafford last season.
'I think the World Cup is the flawless habitat for a player like him to give the best. Why?
In theory, Barcelona would have until the end of the month to sign Pogba before the transfer window closes in Spain. Because it's closed for a month, where he can only think about football.
Pogba's agent, Mino Raiola, is now in England to guide the 25-year-old out of Old Trafford, and negotiations are expected to be fully completed before the window closes next Thursday, according to Mundo Deportivo.
Mourinho dropped Pogba from his starting XI midway through last season amid concerns over his tactical discipline, while the Frenchman argued with his manager over tactics.