I’m not exactly sure what they can do apart from talk - and we don’t actually know what’s going on behind the scenes. But if the player himself and his agent are saying they’re going to do whatever the medical staff says (or maybe he even has his own neurologist), the PA can’t demand anything.
But clearly he now has a compelling concussion history and the Dolphins have a terrible record of diagnosing concussions in-game. That’s certainly something that the PA can make a stink about: why does he keep having concussions in games that he is allowed to continue play?