TOKYO, 6 Oct - England prop Mako Vunipola has ended his five-month recovery from hamstring surgery - but his team's preparations for their final Pool C match with France could be compromised by concerns over the fitness of younger brother Billy.
While Mako, pictured above with England coach Eddie Jones, came on in the 62nd minute of the 39-10 win over Argentina in Tokyo on Saturday Billy, pictured below, twisted his left ankle to temper England's joy at England becoming the first team into the RWC 2019 quarter-finals.
England will carry out a medical assessment of Billy's injury on Sunday, with head coach Jones saying that even if he is forced out of the match, there is cover in the form of flanker Mark Wilson, one of the squad's outstanding performers in 2019.
Wilson does not possess the ball-carrying power of the Saracens number eight, though. and one of the bonuses of having brother Mako fit again is the ground he can make with the ball in hand.
England will be favourites to remain unbeaten in their pool and finish top by defeating the inconsistent French, though Jones is wary of the damage that could be inflicted by the big pack that France coach Jacques Brunel is certain to field for the Yokohama match.
The younger Vunipola had started his 12th consecutive match for England - and his seventh in two months - in the win over 14-man Argentina, who had second-row Tomas Lavanini sent off. "We don't think it's too serious," coach Jones said after Billy's appearance came to an abrupt end.
England need both Vunipolas to take their attack to a new level and Billy always plays better when his older brother is in the starting line-up.
Prop Mako had played just 17 minutes of rugby since injuring his hamstring in Saracens' Heineken Cup final win over Leinster when he feared a recurrence of the problem - against Ireland in a warm-up match - might end his hopes of playing in Japan.
"Yeah i think he had too much Kobe Beef mate"@EnglandRugby head coach Eddie Jones on his sides performance against Argentina and light hearted response to Billy Vunipola question #ENGvARG #RWC2019 pic.twitter.com/MwC8DHHFnh— Rugby World Cup (@rugbyworldcup) October 5, 2019
That is why there was genuine relief when he reflected on his return for England, after replacing the impressive Joe Marler.
He said: "There were days when you are training by yourself when you are thinking, 'Am I going to be back in time?' Thankfully, I have a great medical and strength and conditioning team around me and they are outstanding. Thankfully I got there and it will be a case of seeing how I feel.
"When I injured the hamstring I feared that was it, and I didn't understand what had happened. The scan wasn't ideal and thankfully the specialist cleared it up and it was touch and go with a tough first week.
"I am under no illusion about the things I have to work on and it's now about moving on to the next game. There is always room for improvement and we are happy where we are at the moment but if you settle for that then you can trip over.
"We will look at France who have a massive pack with a good set-piece so we are well aware of the challenge, and I cannot wait to get stuck into the preparations."
Winger Jack Nowell scored one of England's six tries in his comeback game after ankle surgery and also having his appendix removed during one of the training camps in Italy. Vunipola worked with Nowell to get back to fitness, and now believes he is in better shape than ever.
"I lost a bit of weight, the staff and coaches have been outstanding. I feel like I'm in the best shape of my life, body weight-wise, but match fitness is a long way to go. When I came in pre-season, I was 125kg, now I'm 122, it goes up and down.
"It fluctuates, I get a bit too excited - and then eat too much."