If I were the NRL, I would introduce a system where each of the three parties have their own doctor that assesses the players condition (NRL, player, club) and if all three unanimously agree that the player would be suffering great discomfort or risking further injury if they continued playing, that player can be medically retired immediately and their cap space is cleared.
We might see a sudden flurry of medical retirements from across the competition in the first few months as clubs take advantage and clean out all their old busteds, but then I think you would find it would be a fairly rare occurrence once that initial wave comes and goes. I mean to get unanimous agreement, you would have to be completely broken physically e.g JYY, McKinnon, Burgess and Gillett in order to get permission so it can't be abused.
I mean look at it this way, if you had three doctors standing in front of the NRL telling them "Look, if you force this guy to play on, you're putting him at further risk and yourself at risk of litigation.", I don't think the NRL could really say anything else.
