Cardiff - Matthew Rees was on Wednesday ruled out of contention for Wales' Six Nations opener against Ireland after suffering a calf strain.
Rees, who was vying for a starting place along with World Cup hooker Huw Bennett, may also miss Wales' second championship game against Scotland later this week.
Bennett now seems certain to win his 50th cap when Wales line up against Ireland in Dublin on Sunday. With Rees missing, Scarlets team-mate Ken Owens is favourite to earn a place on the bench.
Wales' preparations for the Six Nations have been disrupted by a string of injuries to key players, with centre Jamie Roberts, flyhalf Rhys Priestland and flanker Dan Lydiate all battling to be fit.
Prop Gethin Jenkins and World Cup locks Luke Charteris and Alun-Wyn Jones have already been ruled out of contention as Wales coach Warren Gatland prepares to name his team on Friday.