Wales flanker Ellis Jenkins requires surgery after suffering a "significant" knee injury in their 20-11 win over South Africa on Saturday.
The Cardiff Blues player could now be a doubt for the Six Nations, with his club side issuing an update on his condition.
"Cardiff Blues can confirm Ellis Jenkins sustained a significant knee injury during Wales' autumn victory over South Africa, which will require surgical intervention," read a statement on their official website.
"Further specialist reviews are needed to establish an accurate prognosis following surgery.
"Cardiff Blues and WRU [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."
Jenkins produced an outstanding display against the Springboks as Wales completed their first autumn Tests clean sweep, having already beaten Scotland, Australia and Tonga.
The 25-year-old, who has won 11 caps and skippered Wales to victory over the Springboks earlier this year, received a late call-up off the bench to start after Dan Lydiate withdrew through injury.
He then switched from blindside flanker to No 8 after just 12 minutes of the contest at the Principality Stadium as Ross Moriarty was forced off through concussion and put in a man-of-the-match performance.