Rhys Webb's hopes of a Wales recall against France have received a setback.
The scrum-half has not played for Wales since suffering a serious foot ligament injury during a Rugby World Cup warm-up game against Italy in September.
But Webb, Welsh rugby's player of the year, returned from injury on Sunday as the Ospreys beat Munster 20-17 in Cork.
The 27-year-old, however, suffered a head injury in that victory and is now rated "extremely doubtful" for Edinburgh's Guinness PRO12 visit to the Liberty Stadium on Friday.
"It's disappointing for us but more importantly it's about Rhys," Ospreys head coach Steve Tandy said at his pre-match press conference.
"I don't think it'll keep him out for too long, but with these head injury assessments you've got to make sure that players are at the forefront of these decisions.
"Rhys is extremely doubtful [for the Edinburgh game]."
Scarlets scrum-half Gareth Davies has made a considerable impact in Webb's absence.
But Webb had been hoping to impress the Wales coaching staff this weekend before France's visit to the Principality Stadium on Feb. 26.
Having edged out Scotland 27-23 on the back of a draw with Ireland in Dublin, Wales know victory over France should set up a title decider with England at Twickenham on Mar. 12.
Wales' final Six Nations game is at home to Italy on Mar. 19.