Tensions have been brewing between the two men in recent weeks, coinciding with a run of form that has seen the Red Devils win two of their last five games in all competitions.
Pogba has been subbed twice and left out of the starting lineup three times during that spell, prompting reports of a falling out behind the scenes.
According to The Sun, an unhappy Mourinho accused the £89m midfielder of going through the motions, while also making clear who was in charge at Carrington by pointing at the "manager" sign on his door.
The report also indicates that the France international has regularly been called out in training in front of his teammates, and he has informed his camp to seek possible escape routes ahead of the summer transfer window.
Real Madrid, linked with Pogba before he made his high-profile return to Old Trafford in 2016, are understood to be monitoring the situation.