"I certainly don't see it that way," he said.
"If the worst happens or if things don't work out they're not going to strap me in the electric chair or anything like that. I'll do what I have to but I am a person that goes out there and gives it heaps."
Accompanying Tua was world-renowned boxing commentator Colonel Bob Sheridan, who has spent 49 years covering the sport and has covered 953 world title fights.
He said Tua, who was his favourite heavyweight boxer alongside Larry Holmes, was "fighting for his life".
"If he didn't have problems with business he would have been a multi-millionaire and a multi-world champion - he beat four world champs and he beat two of 'em bad [Michael Moorer and John Ruiz]," said Sheridan.
"I don't usually kiss guys but I kissed him on the cheek and I said, 'David, you gotta win this fight for your retirement'."
He predicted Tua would knock out Ustinov by the fifth round. "Ustinov has no punch, he's not a great fighter."
