Manny Pacquiao arrived at the Police and Citizens Youth Club gym, in the shadows of Suncorp Stadium, an hour late and ready to go to work.

After a spirited session with long-time trainer Freddie Roach, where he ripped pads with the speed that he hopes will give him a clear advantage over Australian challenger Jeff Horn, he was relaxed, jovial and playing air guitar with members of his team.

But make no mistake, Pacquiao has now flicked the switch. During the promotional tour, Pacquiao was expansive, smiling and full of nothing but praise for the venue, the town and his opponent for the WBO welterweight crown.

On Tuesday, he spoke like a man with only one thing on his to-do list. He conceded a rematch with the now active Floyd Mayweather was in the deepest reaches of his mind, but he has eyes only for Horn, the 29-year-old former teacher with an audacious shot at beating a legend.

"If there's a chance, why not. I'm willing but let's focus first for this fight. We don't want to underestimate Horn, thinking about another fight. This fight is not done yet," Pacquiao said.

And Roach, while full of confidence, remains wary. "Jeff could derail us really badly. Manny is in a must-win situation, he wants a rematch with Mayweather. And with Mayweather you have to look good against an opponent, you have to be impressive."

For Pacquiao, now 38 and without a knockout finish since 2009, victory over Horn doesn't appear to be enough at this stage of his career. He will be expected to dominate and while neither Pacquiao nor Roach are big on predictions these days, they are undeniably bullish.

They understand Horn has nothing to lose, while Pacquaio's career will be on the line. Should he lose, retirement is a very real option, while Pacquiao knows how eager Horn will be to take advantage of an opportunity most boxers could only dream of coming to fruition.

"I saw his couple of fights. It's OK. I'm not underestimating him. I'm not taking him lightly. I'm working hard," Pacquiao said. "I remember [what it's like to be hungry]. That's why we did a lot for this training camp. I know what he's feeling ... being there, being the underdog."

Neither fighter talks a great deal before a fight but Pacquiao couldn't resist when asked about fighting a former teacher. He said he would be the one taking someone to school when the bell sounded in Brisbane.

"All I can say is, it's good he's a teacher. Also, I'm a teacher in the ring. We're both teachers," he said.

Pacquiao said he was ready should Horn want to ramp up the tempo from the opening round. Both he and Roach believe the Australian will try and ratchet up the pressure early and have prepared for fast, hard exchanges.

That's a style of fight Pacquiao loves. He was left frustrated by Mayweather's reluctance to trade but expects a far different package from Horn, who believes his size and power can rock the Filipino.

"I'm ready for that. All I want of my opponent is to be aggressive and come inside. All I don't want, I'm not preparing like Floyd Mayweather-style, moving around," Pacquiao said.