British & Irish Lion Jonathan Sexton has been ruled out of action until February as the fly-half recovers from a string of concussions.
Sexton, 29, has been medically banned from playing for a 12-week period as a result of World Rugby and Ligue Nationale de Rugby concussion protocol, which states that any player suffering four concussions in a year are to sit out for that length of time.
His latest clash of heads came in a collision with Rob Kearney during Ireland's victory over Australia last month.
Ireland's first Six Nations match is with Italy is on February 7 and Sexton cannot be cleared to return to contact training before February 8 - just days before Joe Schmidt's men take on France.
"It is most unfortunate and I feel bad for the club," said Sexton, who started all three Tests for the victorious 2013 Lions.
"But I'm still not feeling 100 per cent and with injuries like this it's not worth taking any risks.
"But I'll make sure I come back better than ever, and hopefully make up for lost time when I'm fit to do so."