You don't have to back anyone and it's definitely not the first thing that you do. The first step is to know what is actually happening, why it's actually happening from that point you can say what is truly unacceptable. The reason I tell you that is because I have seen it at professional level in Rugby, I knew people inside the MHR and they would tell me things about Galthier that the press never shared, he was rude to everyone from the receptionist to the players, he was late all the time and would never take any sort of responsibility, all of that was behind the scene so when people started to hear about players unrest they turned against them not knowing what was actually happening.
Funnily enough, people only started to talk about it when he did the same thing in the next club, for years he was supposed to be the victim of the players and the owner.
So what I'm saying is fairly simple, if Pogba has no good reason for his comment then you can be as harsh as you want, if he has a good reason you can punish him, with a fine for example, but also understand and acknowledge the context. What you can't do is act as if context was irrelevant, that's bad management. I will insist on this, I'm not choosing sides I don't care who is right or wrong, I just want the actual issue to be fixed appropriately.