The former trainer of Jeff Fenech and Kostya Tszyu has backed Jai Opetaia to prove himself Australia’s finest ever fighter.

It was Johnny Lewis who oversaw the peak years of the careers of the retired junior-welterweight champion Tszyu and the former featherweight, junior lightweight and lightweight champion Fenech – both so successful that they are widely considered Australia’s finest fighters of all time.

On Sunday Opetaia, the IBF cruiserweight champion, fights Brandon Glanton in his first contest since signing for Zuffa Boxing and the first that will have a Zuffa Boxing title on the line.

The 30-year-old Opetaia has made little secret of his desire to become the undisputed champion in one of his weight division’s most competitive eras, and it is that – and therefore, officially, supremacy over Glanton, Noel Mikaelian, Gilberto “Zurdo” Ramirez and others – that the respected Lewis believes he needs before he surpasses Tszyu and Fenech as the best of all.

“I think he [already] is now,” Lewis told BoxingScene. “He’s great. Mate, you look at that kid at 17, he won the world amateur boxing championship – 17. The Cubans; all of them in there. 

“Far greater wins; prestigious; surpassing an Olympic gold medal, and he did that at 17, and he hasn’t lost a professional fight. I think he stands tall. It might be a little bit too early to say that but I know he will be.

“Just experience. Just experience, and it’ll all just fall into shape for him.”

Asked if Opetaia is therefore already the best cruiserweight in the world, Lewis responded “Yes”, and then explained that he expects to see him move to heavyweight once he has fulfilled his ambitions at 200lbs.

“The way it’s going, you can’t blame him, the money they’re getting to do it,” he said. “Just to see how much he can put on that shouldn’t be there. Anyone can put 14lbs on, but is it good?

“His mother – we all come from Erskineville [in Australia], and his mother was born there. Her mother and brother, we were school friends right through. 

“I don’t think it’s the greatest ever [era of Australian boxing], but I think the two Tszyu boys [Tim and Nikita] are great for us, and certainly, Jai’s exciting.”