The Red Devils paid big money to snare Pogba away from Italian champions Juventus two years ago, but he has been subject to criticism at Old Trafford, while there are also question marks over his relationship with Jose Mourinho.
Pogba was linked with a switch to Barcelona after the World Cup, and the midfielder's agent Mino Raiola reportedly flew to England to present United with the La Liga side's offer.
Juventus are in the market for a new midfielder and have been informed of the availability of Pogba.
Instead of praising Pogba's performances, Mourinho urged him to "understand" why he had done so well in Russian Federation and appeared to suggest the player lacked the same focus for his club.More news: How to use the new app switcher in Android Pie
"There are a lot of names that always get circulated around in the rumour mill - all of them are good players and we respect them themselves but we also respect the clubs they are now at". I think the World Cup is the ideal habitat for a player like him to give the best.
Earlier this week, there was talk of Manchester United looking at Mina. Where he's with his team on the training camp, completely isolated from the external world, where they focus just on football, where the dimensions of the game can only motivate.
In theory, Barcelona would have until the end of the month to sign Pogba before the transfer window closes in Spain.
United can still receive offers for players after Thursday, but will not be able to pursue targets to replace Pogba. "It's about him giving the best he has to give".