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Billy Vunipola needed treatment before being withdrawn from England's win over Argentina

2019 Rugby World Cup Hosts: Japan Dates: 20 September to 2 November Coverage: Full commentary on every game across BBC Radio 5 Live and Radio 5 Live Sports Extra, plus text updates on the BBC Sport website and app.

Doubts continue to grow about the fitness of England's talismanic Billy Vunipola after the number eight sat out training in a surgical boot on Tuesday.

Vunipola was taken off at half-time in the 39-10 win over Argentina on Saturday with ankle pain.

The 26-year-old is now a serious doubt for England's final group game against France this weekend.

"He's been in and out of the boot," said England's attack coach Scott Wisemantel.

"We rested him today [Tuesday] at training - at this stage he's available for selection, but if there's any doubt then we'll rest him.

"We'll make a call on Wednesday night on whether he's fit to play or not."

The younger Vunipola brother - elder brother Mako has just returned from injury himself - is arguably England's most important player, the only specialist number eight in Eddie Jones' 31-man squad and a man whose ball-carrying is essential to Jones' preferred way of playing.

Tom Curry switched from blind-side flanker to the back of the scrum during the second half against Argentina and could play there again if required, while Mark Wilson - who impressed there during last year's autumn internationals - is short of game-time having been injured for the first fortnight of England's time in Japan.

Open-side flanker Sam Underhill told BBC 5 Live: "Billy would be a massive loss but we'd be in a pretty good place with the strength in depth that we've got.

"Billy's a fantastic player and brings such a unique skill set to the game, but we've got a diverse group.

"The back row is about balance, and within that group any of the combinations would work pretty well."

Wisemantel confirmed that the results of a scan on Vunipola's injury are with the team's doctor, but a day after scrum coach Neil Hatley had told journalists Vunipola had not been in a boot, there has been no public word on what the scan may have shown.

Captain Owen Farrell and hooker Luke Cowan-Dickie also missed training, but are expected to recover in time to feature in Yokohama.

Wisemantel said: "Owen's just had a little bit of a stomach virus, both he and Luke.

"I don't know where they've gone, they've probably gone to some little noodle place and got unlucky."

England are already through to the quarter-finals and will top Group C if they prevail against France.

That is likely to give them a quarter-final against Australia in Oita in 11 days' time, four years on from being knocked out of the World Cup at Twickenham by the Wallabies.

With New Zealand possible semi-final opponents for the winner of that tie, some have suggested that defeat by France - and a route into the opposite side of the draw, where Wales and potentially South Africa lie in wait - may be a preferred option.

But Wisemantel said: "Hand over heart, the next big thing is this weekend. It's such a tough tournament if you look far ahead you'll get lost.

"I don't think there's right or wrong side of the draw - you've got to adapt."