Wales star Sam Warburton will miss the entire 2018 NatWest 6 Nations Championship and is unlikely to play again this season after undergoing knee surgery.
Warburton, who has been recovering from a neck operation he had earlier this term, is expected to be sidelined for four to six months, the Welsh Rugby Union said.
He has not played since captaining the British and Irish Lions in the third Test against New Zealand at Auckland's Eden Park five months ago.
In a statement, the WRU said: "Sam Warburton has undergone surgery to resolve a knee injury.
"With Warburton currently sidelined with a neck injury, the proactive approach was taken with a view of ensuring he returns to action fully fit.
"The recovery is anticipated between four-six months."
And Warburton added: "In close consultation with the WRU and Cardiff Blues (Warburton's regional team), we decided it would be proactive to have surgery now on a knee injury, and I am looking forward to returning to action fully fit."
Flanker Warburton, 29, has played 74 times for Wales and led the Lions on their last two tours -- Australia 2013 and then New Zealand.