England No 8 Billy Vunipola pulled out of the Rugby World Cup on Monday because of a knee injury suffered in his country's devastating 28-25 defeat by Wales.

The 22-year-old Australia-born star -- who was judged to have had one of his better games against Wales -- is to be replaced by veteran Nick Easter, 37.

"It's so unfortunate for Billy but the scan shows an injury which means he can't take any further part in the World Cup," said England coach Stuart Lancaster.

"Billy worked really hard and committed everything to the last three months.

"He is a young man with a bright future ahead of him and I know he will be an integral part of this team for years to come.

"Nick was unlucky to miss out on final selection. He is a specialist number eight and an experienced player. We know he will make a big contribution."

If England lose to old rivals Australia at Twickenham on Saturday they would be on the verge of becoming the first sole host of the tournament to exit at the pool stage.

Easter is perhaps most famous for his remark after England were beaten by France in the 2011 World Cup quarter-finals: "that's £35,000 ($53,000) gone down the toilet." He says the comment was taken out of context.

Easter, who has been capped 52 times and also appeared at the 2007 World Cup, could be promoted straight into the back row against Australia if Ben Morgan is ruled out for another match by his knee problem.
That would represent a remarkable turnaround for Harlequins back-row Easter, who was at Twickenham for the Wales match but only in the role of a pre-game and half-time analyst for watching spectators.

England backs coach Andy Farrell said: "We're all devastated for Billy. He has a four to six week injury on his knee. We all know what kind of player Billy is. He was excellent against Wales but unfortunately he got caught under a maul.

"Nick is an experienced guy who has been there and done it. He's a smart guy who understands what pressure rugby is. He goes straight into contention for Saturday."

Farrell added that centre Jonathan Joseph, whose absence with a chest injury led to Lancaster's controversial revamp of his back division against Wales, was making good progress and could feature against the Wallabies.

However, Farrell warned that lock Courtney Lawes (knee) and scrum-half Ben Youngs (ankle), both injured against Wales, had to prove their fitness over the next two days.

Both England and Australia are to name their teams on Thursday.
Source: AFP