Wales prop Nicky is expected to miss four months of action with a chest injury sustained in the Autumn Internationals defeat to New Zealand.
The Ospreys forward, 20, requires surgery after suffering "a significant pectoral tear" on what was only his second Test appearance.
Ospreys medical performance manager Chris Towers told reporters: "He has had scans and been reviewed by specialists and, following discussions, the decision is that the best course of treatment is for him to undergo surgery to repair the damage.
"He is looking at up to four months' recovery, post-operation."
Scarlets prop Rob Evans has been called up to the squad ahead of Saturday's game against South Africa.
