George North has emerged as a doubt for the Six Nations after being stretchered off during the Scarlets 47-15 defeat by Ulster on Friday.
Flying winger North had to be placed in a brace and backs coach Mark Jones confirmed that he had 'issues' with his head and neck.
Jones said: "I only know what I saw on the replay. He's had a knee to the head and he's struggling with some head and neck issues."
Wales can barely manage another high-profile injury with their list of absentees ahead of the tournament's opening game in early February already a huge concern.
Fly-half Rhys Priestland is out of the competition with a ruptured Achilles and they will have to wrap Jamie Roberts and Leigh Halfpenny, who return from injury later this weekend, in cotton wool to ensure their availability.
The troubles are even worse in the pack where props Craig Mitchell and Aaron Jarvis, hookers Huw Bennett and Ken Owens, locks Alun Wyn Jones, Ian Evans and Luke Charteris as well as flanker Dan Lydiate are sidelined.