Sea Eagle Lach
Sounds like your head is more injured than you think (jokes).I would never expect to be compensated for those head knocks I received.
It would probably come down to what were reasonable precautions given knowledge at the relevant time. Certainly up until fairly recently players were expected (meaning either ordered or otherwise shamed into it) to get up and hide any pain after copping a head whack, in addition to which in days gone by head whacks of various kinds were condoned in the game, aside from the most blatant fouls.
I expect player contracts now will all have to include a disclaimer that the player knows there may be a risk. The ones in danger from lawsuits could be clubs who send players back out when they are obviously hurt (Knights winger McManus may be an example of that?)