Ellis Jenkins will require surgery after sustaining a "significant knee injury" during Wales' November Test against South Africa, his club Cardiff Blues confirmed on Thursday.
Jenkins, who was man of the match in Wales' victory over the the Springboks, was stretchered off the pitch following the match on Nov.24.
Wales head coach Warren Gatland said afterwards that the injury "looked like an ACL", although that has yet to be confirmed.
"Cardiff Blues can confirm Ellis Jenkins sustained a significant knee injury during Wales' autumn victory over South Africa, which will require surgical intervention," the Pro14 side said in a statement.
"Further specialist reviews are needed to establish an accurate prognosis following surgery.
"Cardiff Blues and WRU [the Welsh Rugby Union] have and will continue to work closely to manage Ellis's care optimally. No further comments will be made at this stage."
Wales kick off their Six Nations campaign away to France on Feb.1. The six-week tournament concludes on Mar.16, with Wales at home to Ireland for the final match of the series.