England No. 8 Billy Vunipola has been ruled out for four months because of a right-knee injury, meaning he will miss the November Test series.
Vunipola's club, Saracens, said Sunday he has undergone surgery to repair his meniscus.
Vunipola damaged cartilage in his knee during Saracens' 41-13 win over Sale in the English league on Saturday.
Vunipola had only just returned from a long-term shoulder injury, which forced him to miss the British and Irish Lions tour of New Zealand.
He has been outspoken about player welfare in recent weeks.
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Vunipola will be touch and go for the start of the Six Nations, starting in February 2018.
