Martin Murray believes forthcoming opponent George Groves was left damaged by his knockout defeats to Carl Froch.
Murray (33-3-1, 16 KOs) admits it is not only his career but also Groves' on the line when they meet in a WBA world super-middleweight title eliminator.
The British rivals have had seven failed world title attempts between them and can ill afford another setback at London's O2 Arena on June 25.
But Murray, 33, believes he is in better condition than his younger British rival, who is trying to revive his career after three world title losses since 2013.
Groves (23-3, 18 KOs), 28, was twice stopped by Froch (in 2013 and 2014) before dropping a split points decision to US-based Swede Badou Jack, the WBC champion, last September.
"The Carl Froch fights took something out of him," Murray told ESPN. "He's not looked the same fighter since and got put down and lost again against Jack. There has always been issues with his stamina and he's been hurt a few times now.
"The Froch fights took a massive amount of confidence out of him. When he fought the Italian [Andrea Di Luisa in January], he didn't look right, he looked shot. He didn't have any confidence. He didn't get much back in that fight or against David Brophy [in April], but he didn't show much ambition."
Murray, from St Helens, insists he has not considered whether defeat to Groves will mean retirement for him, as Groves believes it would.
"I really can't think about losing so I can't think about retirement if l lose like he says," said Murray. "I feel I'm only just getting into my prime and he's saying that because he knows if he gets beat it's retirement for him.
"There's as much pressure on him in this fight as there is on me, it's a 50-50 fight, but I'm so confident going into this. I've got so much more to give and I've not even thought about losing. When George gets beat it's him who goes into retirement."
Murray and Groves meet in an eliminator for the WBA world super-middleweight title, held by Germany's Felix Sturm.
Murray held Sturm to a disputed draw in 2011 and was again a points loser in a world middleweight title fight when he travelled to face Sergio Martinez in 2012.
A courageous 11th round stoppage loss to Gennady Golovkin last year -- no one has lasted as long with the Kazakh destroyer -- and then stepped up a division for a split points loss to Arthur Abraham in November.
Murray says he is a more dangerous force operating at super-middleweight and has used an altitude chamber to help him prepare for Londoner Groves.
"Being a super-middleweight now I'm eating a lot better and I'm a lot happier, I can do more in training," said Murray. "I'm going into this fight feeling the best I've ever felt. You are going to see the best Martin Murray you've ever seen, but I don't think you will see the best George Groves there's ever been.
"I've tweaked a couple of things for this fight. I've got my own nutritionist now who is preparing my meals. I've been working at an altitude centre so I go into a chamber that replicates 3000ft altitude where there's less oxygen so it gets your body used to working with less oxygen so you're not going to tire as easily."