London - Wales captain Sam Warburton is facing at least four weeks on the sidelines with an ankle injury, his club Cardiff Blues announced on Tuesday.
"Sam has suffered a grade two strain to his right ankle and has now seen the specialist to start his recovery process," Cardiff's head of medical services John Miles told the club website.
"He will return to the specialist in a week's time for further assessment and currently we are working at a minimum lay-off of four weeks for a return to play."
Warburton, 27, sustained the injury in a tackle by Justin Tipuric, his rival for the openside flanker berth with Wales, during Cardiff's 13-6 Celtic League defeat at the Ospreys last Saturday.
He will miss two European Challenge Cup matches against Montpellier in December, as well as Celtic League derbies against Newport Gwent Dragons and the Scarlets over Christmas.
Wales are due to open their Six Nations campaign against Ireland in Dublin on February 7.