The 25-year-old was linked with a move away from Old Trafford after apparent discontent with Mourinho. But he remained in situ when the window shut last Thursday in England.
The La Liga champions have already added Gremio midfielder Arthur, Bordeaux winger Malcom, Sevilla centre-back Clement Lenglet and Bayern Munich battler Arturo Vidal.
His desire to play for Barca is the driving force behind his wish to leave England’s northwest.
Juventus midfielder Miralem Pjanic is set to sign a new contract at the Turin Stadium, according to Mediaset Premium.
The 28-year-old will add one year to his current deal, which ends in 2021, but his wage will jump to €7 million per year.
The Bosnian international has developed into one of Europe’s best players since he arrived in Turin two years ago from Roma. He’s won two Serie A and Coppa Italias since, scoring 15 times in 91 appearances.
Barcelona, PSG and Real Madrid have been chasing his singature this summer.
The 23-year-old has turned down repeat overtures from the Ligue 1 champions to extend a contract that expires in 2019. This has caused sustained links to Barcelona and Juventus.
However, the Italians giants are prepared to play a waiting game.
The Serie A champions have repeatedly shown themselves to be experts in working the free-agency market. Germany midfielder Emre Can became the latest bargain recruit this summer after his contract at Liverpool was run down.
Liverpool have also expressed interest in the former Pau man.