Ireland outhalf Johnny Sexton is a doubt for Ireland's opening Six Nations game against Italy after Racing Metro said he would be out until 14 February due to concussion.
Sexton has not played since he sustained a blow to the head during Ireland 26-23 victory over Australia on 22 November.
He is believed to have been suffering from nausea and headaches since the injury, and has been seeing a neurologist in Paris about the symptoms.
"He will not play a match until he's 100%," Racing Metro's head coach Laurent Labit told a news conference as Sexton was again left out of the squad for Saturday's Top 14 game against La Rochelle.
French sports daily L'Equipe reported on Thursday that the French league's medical committee had banned Sexton from playing until 14 February, which means he would at least miss Ireland's opening Six Nations game against Italy a week earlier.
The IRFU medical team will assess Sexton themselves either in late December or early January to ascertain the extent of the concussion, and at that point will contact Racing to make an informed decision on what is deemed best for the Top 14 player's welfare.
As the tie with Italy falls within the World Rugby international window, if the IRFU deem Sexton to be fit, then their decision would supercede Racing's.
Ireland's next match falls on 14 February against France at Aviva Stadium, the day that Sexton's medical ban would be due to come to an end.
At present, Sexton is allowed to train with Racing, but only permitted to partake in non-contact activities.