England and Saracens number eight Billy Vunipola will be out for four months with a knee cartilage injury.
Vunipola limped off in the Premiership side's 41-13 win over Sale on Saturday.
The 24-year-old underwent surgery on his right knee on Sunday and will now begin rehabilitation.
The official Six nations twitter had tweeted earlier this week that the back-rower was nearing full fitness after being selected for the England training squad.
Vunipola saw the funny side, tweeting a reply that made us chuckle.
I think I speak for everyone at RUCK when I wish Vunipola a fast recovery!
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