England head coach Eddie Jones has admitted his side do not make the grade when it comes to their fitness.
Jones has challenged the Red Rose players to sharpen up their shape for the challenges that lie ahead after seeing them in action at close quarters and observing their shortcomings.
"They're not right for international rugby, that's the distinction," Jones said.
"They're right for club rugby. They can play club rugby 365 days of the year but international rugby is faster, there's more accelerations, the running speed is higher and you need to have a different sort of training for international rugby."
England have begun their Six Nations quest with wins over Scotland and Italy, and on Saturday they will play Ireland at Twickenham.
After the World Cup embarrassment, where hosts England were knocked out in the group stage, experienced former Australia and Japan coach Jones was brought in to replace Stuart Lancaster.
He is confident of getting the best out of England, and while he says the team are not right at the moment, Jones added: "But we'll get it right in the future."
Speaking on Radio Four's Today programme, Jones said of his England players: "It's quite simple to me that the time we have with them we work them hard, work them at the level we need to, and when they go away to their clubs if they need to do extra work they do it and if they don't do it then England won't be a dominant country."
Jones expects the clubs to be supportive of his ambitions for England.
"They have to assist without a doubt and I've got no doubt English clubs will do that," he added.
"One of the things I've noticed since I've been back is how professional and how well structured the clubs are. They've got strength and conditioning staff and medical staff at rates nowhere else in the world have.
"You've got to remember they're coaching players to be successful at club level, they're not coaching their players to be successful at international level, which is 100 percent right.
"We've got to get them to understand and the players to understand that to be successful at international level there's a plus factor there."