Warren Gatland confirmed Ellis Jenkins may have suffered damage to his anterior cruciate ligament late in Wales' win over South Africa.
Wales flanker Ellis Jenkins looks certain to miss the Six Nations after sustaining a suspected anterior cruciate ligament (ACL) injury against South Africa.
Jenkins put in a man-of-the-match performance as Wales earned a 20-11 victory at the Principality Stadium to make it nine straight Test wins for the first time this century.
However, the match finished with an almost sombre atmosphere in the stands as Jenkins – who was a late call into the starting line-up due to an elbow injury for Dan Lydiate – received medical attention in the closing stages.
Jenkins will have a scan on Monday but is now unlikely to return for the Six Nations, which starts in February, while he could also be a fitness doubt for next year's Rugby World Cup in Japan.
"I don't know how he is. There will be a scan on Monday. It looks like an ACL which is not brilliant," head coach Warren Gatland said after the game.
"He's very disappointed. His performance was outstanding. Before the game, I had a one-on-one with him. I thought he was excellent.
"I thought today was an outstanding performance and he deserved Man of the Match. You have to really feel for him.
"When anyone gets injured it's the hardest thing to take. You know it's a big year for a lot of players and they work so hard.
"He was co-captain on the summer tour and he did a great job.
"When you see a player who has worked hard to win his spot and get in the team, pick up an injury, you feel for him."
On Wales' overall performance, Gatland believes his team are still a work in progress despite their terrific run.
"It was the toughest game we've played this autumn. There are aspects we need to challenge the players on and challenge themselves technically," he added.
"They can go away with their regions and get away with things, but when you play the best teams in the world you can get exposed.
"There is some game management we can improve. The good thing with these guys is they can dig themselves into a hole and then get out of it.
"We're in a good place at the moment. I don't think we've lost at home this year. That's a nice feeling in the changing rooms. But we know there's a lot of work to do."