We've seen several current and former players mention that when a player gives the team doctor permission to work on them they waive the right to sue. I'm sure somebody with more legal expertise and a better understanding of the CBA than myself will have more insight but it sounds like players say they have no right to sue.
Before anybody goes where I know they'll go with that statement the opposite would end up happening. If teams don't provide their own doctors people will bitch that the teams are cheap and can't provide medical care. If they do and somebody does something they don't like, that the players give consent to have done, then the teams are disgusting and pathetic for forcing a player into taking treatment. It's one of those things that are a no win situation that society forces people/organizations/companies into with their own ideals.