WBA and IBF super-middleweight title challenger George Groves insists he has the physical fitness to match Carl Froch over 12 rounds - but has questioned whether the defending champion has the mental toughness needed.

The pre-amble to this weekend's record-breaking fight has gone into overdrive and Froch admitted on Monday he does not enjoy the build-up.

Groves was keen to seize on that as a sign of weakness and told his opponent Saturday's rematch in front of 80,000 at Wembley is one he cannot win.

"Technically, in a purely boxing sense, I beat Froch every day of the week," he said.

"Saturday night is fast approaching and he needs to get himself up for this fight and I wish him luck because he is in a fight he can't win.

"It is not because he is not good enough but (because) I won't allow him to win.

"If he wants to fall apart mentally, so be it. If he needs to coach himself to not fall apart, I wish him the best of luck there too.

"I'm sure he's felt good at times and I'm sure he's felt vulnerable at times.

"It is sink or swim time in terms of whether you deal with the occasion or not but I've never failed yet.

"I've boxed in front of big crowds and I've never let the occasion get to me and it is all about containing the excitement not the nerves.

"Nothing is left to chance with me. We are in fight week now and he needs to understand his destiny is dawning."

Six months ago the 36-year-old Froch beat his younger rival in Manchester but had to drag himself up from a first-round knock-down and weather a severe storm before controversially stopping the Londoner in the ninth.

Groves warned this time around he is more than capable of going the distance, having benefited from the expertise of trainer Paddy Fitzpatrick, although he is confident that will not be required.

"It may sound a bit strange but I've never had a full-time conditioning coach there for every session like I have this time," he told Sky Sports.

"Paddy has really been able to get involved and stamp his authority on the sessions and we are in the gym hitting targets we have never reached before.

"I think Carl Froch is certainly banking on the fact he thinks he's a 12-round fighter and thinks that I'm not but he's in for a rude awakening.

"I'm fitter than ever and 12 rounds will be a breeze.

"The fact of the matter is that if Carl can withstand punishment past six rounds then it's only going to get worse for him because I'm only going to get stronger, fitter and faster.

"I know I can go more than 12 rounds if need to but the fact is I don't think Carl Froch will go past three."

American Charlie Fitch has been confirmed as referee despite a reported a late objection.

"We have right of approval over officials and if we didn't want a particular referee he wouldn't be working on Saturday," said Groves when it was put to him it was his camp who had objected.

"The first referee was objected to by Froch's team or Matchroom (promoters) but we wanted a strong referee who won't take any rubbish.

"We brought up the fact Froch likes to foul and we wanted a strong ref.

"If my team are happy with Charlie Fitch then I am. He is a well-respected referee from New York.

"I'll give him an easy night's work, no problem."