If there is a fitness doubts new players need to be on a pay/play contract then there is an incentive not to be a permacrock.
I do wonder what goes on in some people’s heads. Listen to virtually any retired footballer and they will tell you that they were never fully fit after their first game, they play most of their careers with some sort of injury.
Take your approach and you’re more likely to get players playing with an injury and letting down the side because they’re worried about getting paid & putting food on their kids’ table.