Do y'all actually understand what "the players can't sue" means? Or are y'all just parakeeting that from a quick Tweet?
I'd think regardless of what was signed that any professional can still be sued - like if a Dr. used the wrong medication on someone, injected poison instead of medicine, etc. Very rarely does a "can't sue me" condition in a contract mean that people can do just ANYTHING without consequence.
With that being said....it sounds like this might be a known risk factor for whatever the procedure was. No medical knowledge on my end to know this tho.