Englands Billy Vunipola set for four months out putting Six Nations chances under threat

England number eight Billy Vunipola faces a race against time to be fit for the start of the Six Nations after undergoing knee surgery.

Vunipola has been ruled out for 16 weeks with the cartilage damage sustained in Saracens' 41-13 Aviva Premiership victory over Sale at Allianz Park on Saturday and will miss England's autumn series against Argentina, Australia and Samoa.

"For any team to lose a player of the ability of Billy is a blow and he will be missed through the autumn for both Saracens and England," Saracens director of rugby Mark McCall said.