Dan Biggar suffered another injury blow during Wales' 29-17 win against Fiji on Wendesday.
The Saints fly-half, who had shrugged off the concussion he sustained against Australia on September 29, was forced off in the 56th minute of the match.
Biggar was involved in a horrible collision with team-mate Liam Williams as both players tried to gather a high ball.
Williams came off unscathed but Biggar, who had earlier produced a sublime assist for a Josh Adams score, was floored for some time before eventually being able to get up and run off the pitch.
He did not return to the game and Wales, whose next match is against Uruguay on Sunday (kick-off 9.15am UK time), will now hope there are no lasting issues.