Owen Franks insists he is in great shape ahead of his switch to Saints.
The 31-year-old tighthead prop was a surprise omission from New Zealand's 31-man World Cup squad.
Angus Ta'avao and Nepo Laulala were given the nod, leaving Franks out of the picture for the upcoming tournament in Japan.
He will now focus on playing for Canterbury before moving to Saints on November 1.
And Franks insists he is in even better shape than when he helped the All Blacks to win the last World Cup.
"The frustrating thing is that there's talk out there that I'm slowing down and age has caught up with me," Franks said. "I really don't buy it.
"I think I'm much better shape, possibly even better than the last World Cup.
"I'm not just comparing myself to Angus and Nepo – those guys thoroughly deserve their spots and to be fair they have got a bit of pace on me."
And he added: "If I compare myself to me three years ago, there's no doubt I'm moving better and I am in a lot better shape.
"I have worked pretty hard at that. I have always been pretty honest in my self-assessment. I am harder on myself than what anyone else is, or what feedback they can give me – I have probably already given it to myself."
Franks says he feels a lot more mobile since having surgery on an Achilles tendon in 2017.
The injury forced him out of the Rugby Championship and Northern Tour while managing the pain with painkillers.
"Before that, it was up to years on end of dealing with it," he said. "Probably up to 2017 I was at my worst in terms of mobility, running wise.
"And I feel I have been re-building since then and going from strength to strength.
"That's why when I hear that I have been slowing down in the last couple of years, it's just plain wrong.
"I know where I was at a few years ago. I had to have painkillers just to be able to run, I was running like s***.
"Now it is totally different. I still have a long career ahead of me."