All Blacks and Crusaders player Ryan Crotty suffered his sixth concussion in 18 months during the Bledisloe Cup opening match against Australia on Saturday night.
Crotty was helped off the field early in the first half.
Laura Fergusson Trust rehabilitation director Katie Hodge said it would be risky for Crotty to keep playing rugby after the concussion.
She said this was Crotty's sixth head-knock in a short time-frame.
"I think it would be risky to go and play again."
Hodge said the long-term consequences of concussion included ongoing headaches, dizziness and brain tiredness.
Hurricanes players Reggie Goodes and James Broadhurst both retired from rugby on medical advice, as reported by Stuff, because of multiple concussions.