That's not how it works though. If a player is unhappy with something, or the team is having issues, they have every right to speak about it. Especially the most experienced and those considered to be leaders. They are people, not sheep. And a dressing room has to work in harmony with the manager.
We don't really know what happened, since this is one side of things, but Varane has a lot of credit in the bank because of the career he's had and how he's conducted himself through it.
He has won it all in his career, and from start to finish has always been said to be an absolute professional.
If anything, he did what he was supposed to do from this standpoint. If the squad is unhappy about something, you tell the manager that they're unhappy. He didn't leak it, didn't down tools, he brought up the subject, as he should.