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Billy Vunipola fears more gruelling training sessions when he steps into the unknown for England's first camp under new head coach Eddie Jones.
Jones, who is talking to Jonny Wilkinson over the possibility of the World Cup winner joining his coaching team on an informal basis for the RBS 6 Nations, wants to hear his players complaining, knowing it means his methods are working.
Vunipola will start at number eight against Scotland on February 6 but must first endure two weeks of preparation at the squad's Surrey training base while recalling the effort it took to shed seven kilograms during last summer's World Cup training camp.
"I'm not too sure how to read Eddie Jones at the moment. He's very direct, from what I've heard, and that probably could be his best asset," Vunipola said.
"Hopefully he will take us forward and I'm looking forward to working with him and the coaches he has appointed.
"I've spoken to him on the phone and the few things he has told me to work on I'm doing my best to improve.
"I do agree with what he says - I can't really say I don't because I want to play!
"There is an excitement, but there is also a lot of hard work ahead. He has mentioned what is to come himself, so I'm a bit nervous about what that is and whether it's mental or physical.
"What scares me the most is that Denver last summer was my breaking point, so if he takes us to that place again it is not going to be fun at all! But I definitely won't be complaining."
For two years Vunipola has duelled with Ben Morgan for his place in England's back row, but now he must see off a new contender.
Morgan was omitted from the 33-man squad for the Six Nations announced on Wednesday, with Jones revealing that he views Harlequins' Jack Clifford as primarily a number eight.
The two played for England at junior level and it was Clifford who kept Vunipola out of the team during the 2012 World Rugby Under-20 World Championship, although the Saracen has since won 23 caps while his rival has yet to make his Test debut.
"Jack can make the step up. I played in the same team as him in the age groups and I couldn't get into the team," Vunipola said.
"Whether it is at six, seven or eight, he is a very good player. He has got a bit of everything and his strength is in his speed. I'm sure when he gets his chance he'll do really well.
"I wouldn't say it is a rivalry because we have always tried to help each other. He is a great guy, but it was the same with me and Ben Morgan when we went into camp and were trying to get into the team."