9. Pete Browne
The Ulster second-row announced his decision to retire from the game, with immediate effect in October 2018, after suffering repeated concussions. The 30-year-old revealed that he met with a neurological specialist who helped him realise that hanging up his boots was the right thing to do.
10. David Denton
IIn September 2019, the 29-year-old has been advised to quit following a concussion injury he sustained playing for Leicester Tigers in October. Zimbabwe-born Denton was capped 42 times for Scotland, making the move to Edinburgh Rugby in 2010 before spells at Bath and Worcester Warriors proceeded his switch to Leicester last year.