England have encountered the first major injury problems of their World Cup campaign after it was revealed that Jonathan Joseph and Ben Morgan are doubts for Saturday's pivotal clash with Wales.
Joseph took a bang to his chest in the 35-11 victory over Fiji while Morgan is struggling with a knee problem. Both players must prove their fitness today before the team is announced the following morning.
"Jonathan has a bit of a knock, nothing too serious and our medical staff are working extremely hard behind closed doors to get him fit for selection," backs coach Andy Farrell said.
"We will give him every chance to put an England shirt on this weekend.
"It's something and nothing. He has got a knock on his chest. If he is fit for this weekend, we will know by tomorrow internally. If he is not fit it will not be more than a week anyway probably.
"Ben has a little bang on his knee that isn't serious at all. There are still a couple more knocks, people who are not serious. We'll leave them unnamed. Some guys will train today, some guys won't train today. We'll see what happens over the course of today. We don't need to rush.
"We need to take our time and give everyone the best possible chance of being fit. People have got bangs and long-term injuries who need a couple more days."
Joseph is England's main threat in midfield and his loss would be a blow to the hosts' chances of placing one foot in the quarter-finals by toppling Wales.
Brad Barritt could move from 12 to 13 to fill the void, while Henry Slade and Sam Burgess are also possibilities. Owen Farrell is an option at inside centre and in training on Monday a trio of Farrell, Barritt and Burgess was fielded.
If Morgan is ruled out, head coach Stuart Lancaster would face a simpler choice with Billy Vunipola starting at number eight and James Haskell elevated to the bench.
The midfield permutations are numerous and have increased after Farrell declared Sam Burgess is a genuine option to start despite having played only 112 minutes of Tests rugby.
Burgess impressed as a final-quarter replacement against Fiji when his direct running helped restore momentum to a team that was drifting, but starting against a Welsh centre combination including Jamie Roberts would be a big ask.
"We were confident when we picked the 31-man squad that everyone could do a job for us and we have to make sure everyone is comfortable in starting," Farrell said.
Wales will arrive at Twickenham with injury problems of their own and Farrell expects their coach Warren Gatland will be creating a siege mentality to inspire the underdogs.
"'I've absolutely no doubt Warren will be doing that. We're still waiting for our team talk from him!" Farrell said.