Australia's most decorated boxer says he "won't be surprised" if Gallen beats Huni in their much-hyped bout in Sydney next month.

Both are undefeated and both are brimming with belief, but that's where the comparisons end with Huni - the first and only man in 120 years to win the Australian heavyweight title on his professional debut - widely considered a class above Gallen, the rugby league great turned pugilist.

Even Gallen accepts he can't out-box his 22-year-old opponent, admitting his only realistic chance of beating the supremely sharp and skilful Huni is by knockout.

But if Fenech says Gallen can win, others ought to listen.

And the triple world champion believes Gallen has achieved enough in defeating UFC legend Mark Hunt and Australia's only ever world heavyweight champion Lucas Browne last month to at least command Huni's respect.

"He has a huge test this time because Justis is one of most skillful guys I've seen," Fenech said on Tuesday.

"But I also had lots of those thoughts thinking Lucas could do certain things and Gallen stopped him in round one by his sheer willpower and mental toughness.

"It's going to be a tough fight for Justis, it will be a tough night.

"I'm sure they will be both be prepared. I can't wait to see what happens.

"I wouldn't be surprised If I'm surprised again."

Billed as boxing's State of Origin, promoter Dean Lonergan claims Gallen has less chance of beating Queenslander Huni than NSW had of taking a series off the Maroons under Cronulla's premiership-winning captain.

"I think once in eight or nine Origins he won," Lonergan said.

"Paul's in a whole world of pain.

"Paul's been in the entertaining/circus fighting game. Now he's in the hurt game and it's a whole different ball game.

"Justis is going to inflict a lot of pain and he's (Gallen) going to find out what it's like with a real boxer."

Straight-shooting Gallen readily acknowledges he faces the greatest challenge of his 12-fight career.

But the 39-year-old says he's indeed ready to shock Fenech, Lonergan, Huni and the rest of the boxing world, just as he did with his brutal first-round KO of Browne.

"Me and Jeff have a relationship; he knows me and he does care for me a little bit," Gallen said.

"He did come to me about the Lucas Browne fight and was concerned.

"He spoke to me openly and a little bit concerned and I said, 'Jeff, I will be OK.' I surprised him there.

"I know deep down he thinks Justis will win but I'm here as he said to surprise him and everyone again.

"I train my backside off, I work hard, I get in the ring mentally prepared.

"I haven't faced someone like Justis before, I agree with that. I haven't faced someone with his speed and talent, I agree with that.

"But he hasn't someone like me, I promise you that.

"I've been a professional athlete for over 20 years.

"There's a reason I've been a professional athlete for over 20 years and that's because of the preparation I do.

"When I get in there I will be 100 per cent prepared."

Australian Associated Press