Horn is seeking his first world title against Pacquiao, who was already a world title holder by the time the Australian Olympian turned 10.
Roach, who has guided Pacquiao for the majority of his career, said Horn would notice that the most through Pacquiao's hand speed.
"With Mayweather, you have to look good against an opponent, you have to be impressive".
He then spoke to reporters and issued a veiled warning to Horn - a former Queensland school teacher - describing himself as a "teacher in the ring".
Pacquiao, who was outpointed by Mayweather in the "Fight of the Century" two years ago, will be the strong favourite when he defends his world title against the unbeaten Horn in Brisbane. Horn (16-0-1, 11 KOs) fought three times in 2016, winning all three bouts by stoppage.
He's most risky when he's attacking from the side and he is constantly rehearsing the shock punches. I was talking about Manny's fight coming up and he said "I fought him in the amateurs".
His most unsafe technique will be to slip underneath Horn's left jab, then from a crouch position take a little jump to Horn's left, then a little step to the right and try to nail Horn with a right hook and the booming straight left cross that has been the big knockout weapon throughout his career.
"I know my body".
"I expect Manny's best in this fight". It's the way we've always worked.
BRISBANE, Australia (AP) - Freddie Roach is ready to narrow down Manny Pacquiao's options following the WBO welterweight championship fight against Jeff Horn: Think about another shot at Floyd Mayweather, or think about retirement.
"This is Jeff Horn's big chance".
And Roach knows that Pacquiao needs to produce a classy performance in order to catch Mayweather's eye. If he will be able to do so against Horn remains to be seen.
Jeff Horn (left) trains with Glenn Ruston during a training session in Brisbane, on Monday, June 26, 2017. I look at his eyes between rounds to judge his spirit.
Horn is known to possess a powerful overhand right, which his camp claims will be the key weapon against the southpaw Pacquiao.
"With his foot movement, Manny's impossible to catch, " Fortune said. Manny is, I think, in a must-win situation.