Polwart, 24, announced this morning he woun't take part in next year's Super Rugby season after deciding it wasn't worth the risk.
“It has been a difficult decision to make to leave the game I love," Polwart said.
"It has provided me with plenty of great friendships and some awesome experiences. I have had some on-going issues with concussion, and while I am currently symptom free, I chosen to hang up my boots and not to put myself at further risk.