Wales flanker Sam Warburton will miss the upcoming autumn internationals as he requires surgery on a long-standing neck injury.
The two-time Lion, who captained the side in Australia in 2013 and in New Zealand earlier this year, has been ruled out for up to four months after aggravating the injury during training earlier this week.
"Sam Warburton will undergo surgery following a recurrence of a long-standing neck injury," Cardiff Blues said in a statement on Tuesday (12 September).
"The Cardiff Blues flanker, who led the British and Irish Lions to a drawn Test series with New Zealand in the summer, exacerbated the injury in training this week.
"He has undergone scans and has been reviewed by a consultant, who confirmed the management plan. It is likely that Sam will miss a period of up to four months."
The 28-year-old, who is yet to feature for his club this season after taking an extended break after the Lions' tour, will miss out home Test matches against Australia, Georgia, New Zealand and South Africa between Novermber and December.
His absence is a major blow for Warren Gatland, as it leaves a gaping hole in Wales' back row, with fellow Lion Justin Tipuric expected to wear the number 7 shirt for the four autumn Test in place of the former Wales captain.
The flanker will also sit out a host of Pro 14 and Challenge Cup matches in what is the latest injury setback for the for the Blues, who have already lost back rowers Ellis Jenkins and James Botham for up to four months with a hamstring and ankle injury respectively.
The Blues, who have started the season on the back foot and lost their first two games, are left with Josh Navidi as the only senior specialist open-side flanker.
Warburton, who has 74 caps for his country, missed three weeks in October last year after fracturing a cheekbone and faced a race against the clock to be ready for the summer tour to New Zealand after missing six weeks at the end of last season with a knee injury.
However, he is expected to be fit in time for Wales to start their Six Nations campaign at home against Scotland on 3 February next year. Gatland's men then face back-to-back trips to Twickenham and Dublin, before hosting Italy and France in the final two games of the tournament.