Australian challenger Jeff Horn has made a massive blunder by not training against superior sparring partners in the United States in preparation for Sunday's title fight, Manny Pacquiao's team says.

The legendary 38-year-old Filipino, one of the greatest fighters of his generation, is widely tipped to overcome the unbeaten Horn in front of an expected 50,000 people at Brisbane's Suncorp Stadium.

Pacquiao's Australian strength and conditioning coach Justin Fortune said on Thursday the 'Fighting Schoolteacher' hasn't done his homework and will be outclassed by the master eight-weight world champion.

"Manny is one of the greats and Jeff Horn is in a different league," former heavyweight Fortune told reporters.

"If Manny puts his mind to it he destroys anybody in the world. He's busted up some of the greats. Jeff Horn is the guy to knock out and we're in the hurt business."

Fortune, who once fought against Lennox Lewis, said Horn should have spent eight weeks in America against the best available sparring partners.

"Then you might have given him a real shot if he'd been training with A-grade guys all the time," he said.

"Instead he's been using (Filipino) Czar Amonsot as a sparring partner and he is nowhere near as fast as Manny.

"Horn won't know what hit him because Manny is that quick."

- Inexperienced Horn -

Fortune said he gave Horn no chance of causing a major boilover against the warrior known as 'Pac Man'.

"People say 'well, Manny hasn't knocked anyone out in years' but these are AAA guys, with pro-level experience, current or former world champions," Fortune said.

"This guy (Horn) has nowhere near the experience at all. He hasn't walked out in front of 50,000 people, ever.

"Nerves take a lot out of you when you fight. It's actually terrible, there's nothing you can do about it, happens to all of us.

"Manny's done it, he's used to it, it's no big deal. Jeff's not. I don't think they've realised that."

Horn defended his training strategy, saying he was more than happy using Amonsot, who is ranked number three with the World Boxing Association at junior welterweight (140lb, 63kg).

"It's very hard for anyone to copy the style of Pacquiao but we got the closest thing out there that we could," Horn said.

"I've definitely sparred the best I ever have for this preparation and I'm really happy with the rounds Czar gave me."

Horn said while Pacquiao might be faster than him, he had an awkward style that the Filipino has not faced before.

"My style will give him problems and it's a matter of timing him so that I can make him miss and land my hard shots," he said.

Pacquiao (59-6-2, 38 knockouts) is one of the greats, while Horn, 29, has won 16 of his 17 bouts with one draw.

Pacquiao, who briefly retired last year before making a successful comeback against Jessie Vargas in November, has not stopped an opponent since his 12th round TKO of Miguel Cotto in 2009.

Trainer Freddie Roach has suggested Sunday's fight is a stepping stone for Pacquiao to secure a rematch with American rival Floyd Mayweather, who outpointed the Filipino in the "Fight of the Century" two years ago.