The Aussie has fought against the odds all his life and admits he is lucky to be alive after suffering chronic asthma as a kid.
There were times when his parents came close to losing him, but the fighter inside saw him through more than his fair share of dark days.
He revealed: "I had a lot of really bad asthma as a kid, being in hospital, missing school. Sport was one thing I was good at but I was always in trouble with asthma. I am still a bad asthmatic brought on by allergic reactions and not exercise.
As a kid it wasn't easy with the asthma but it is something that I have learned to live with.
I learned to live with disappointment but number one is my health. I carry my asthma medications with me everywhere, I won't leave the house without it, that's how it is for me these days. I carry my inhaler with me everywhere, even if I am just going to the shopping centre, just in case...
I was in hospital a lot as a kid, basically sitting on the bed with the machine that helps asthmatics breath there. It was to keep me going. There was one occasion when I was about 15 and I was rushed to hospital so they could pump me full of drugs to keep me alive.
I suppose you could call it uncontrollable at the time and maybe that is why I am so obsessed with carrying my meds with me everywhere. For some reason I never really worried about it as a kid - I developed an 'if it happened it happened' mentality. But looking back now, there were a lot of close touches.
De Mori even took the drastic step of quitting Australia to live in Croatia because his condition eased considerably there.
He explained: "Now I am living in Croatia in a city called Split and one of the main reasons is that my asthma is much better there.
In Australia it is a lot worse, certain places I go, I notice within the first three hours how my asthma is going to be.
Why is it better in some place than others? Well I guess it is to do with the pollen from the flowers or the trees and dust as well. I just have to be really careful."
De Mori knows he will have to be really careful against Haye, and that he doesn't get caught cold on the Hayemaker's ring return after three years out.
He said: "Haye is obviously the favourite and everyone knows who he is. Even if I am extremely nervous before a fight I know what my character is and as soon as that bell goes, I just fight with all my heart.
I've gone into fights with injuries that I've hidden but still fought with my all my heart. Whatever the pressure or people booing me the bell goes and I give my best.
We have all seen fantastic fighters who have the athletic ability, stamina, strength and size but they can't handle the big time atmosphere, the big moment and they just crumble. I guess I have an inner confidence to fight.
I know Haye will come out and hit me with a shot that will hurt but he is going to feel me fight back.
I won't be falling over or looking for a way out. I won't be charging in there with my chin hanging out.
A lot people over look me because they don't know me. But when they watch me spar, they know I have a good jab, a good defence and am very crafty.
If people want to believe I am limited because of the way I am built, they don't really see the other qualities I have. That suits me. It's the biggest fight of my life, not the biggest of Haye's, not like when he fought Wladimir Klitschko.
Now he has a new trainer, three years out, maybe a bit rusty...who knows what will happen when the first bell goes?"