The 26-year-old suffered a blow to the neck which affected a nerve in his arm during the Scarlets’ RaboDirect PRO12 semi-final defeat to Ulster last week and won’t recover in time to take part in the tour.
Newport Gwent Dragons hooker Sam Parry was called into the training squad earlier this week.
Head Coach for the Japan tour Robin McBryde will name his final 27-man squad on Tuesday 21 May.
