Mathias Pogba has lifted the lid on the relationship behind the scenes by claiming the former manager's ego dominated the dressing room and created unrest.
Pogba himself has been accused of having a big ego, which contributed to a fragile relationship with Mourinho, but his brother says it was all the Portuguese's fault.
Pogba has flourished in the few games since Mourinho left, which could add weight to his brother's claims.
"It was Mourinho who was the problem," Mathias Pogba told RMC Sport. "Mourinho still wants to be the centre of attention. The problem was Mourinho, right down the line.
"In the locker room, outside the locker room everything, I know my brother, and you tell him, 'Go. Go play ', the rest, he will do it.
"From what we see of Mourinho, he always wants to be the maestro, the centre of attention.
"(Paul) does not even calculate that aspect: you respect him, he will respect you, you trust him, he will produce big performances."