Justin Tipuric is facing three months on the sidelines with the Welsh flanker still suffering symptoms following his concussion against Italy in the Six Nations.
The diagnosis rules him out until the start of next season - meaning he will play no part in the tour of New Zealand in June.
Irish outhalf Johnny Sexton was given a similar three month layoff early last year due to concussion symptoms.
The Ospreys openside flanker will also miss out on the Great Britain Sevens squad for the Olympics in Rio with the injury ruling him out of the build up for the games.
Tipuric was kept in hospital overnight after an awkward fall from a lineout in Wales’ heavy win over the Italians last month.
Ospreys medical performance manager Chris Towers said: “Justin is recovering well following the concussion suffered playing for Wales against Italy three weeks ago, but in the light of his symptoms the specialist advice is that it is in his best interests to take his time returning.
“A prolonged three-month period of recovery rules him out of the rest of the season for the Ospreys and the Wales tour to New Zealand. The focus for Justin will be on getting healthy and fit, ready for pre-season.”
