If eight division world champion Manny Pacquiao (59-6-2, 38 KOs) intends to once again draw the big crowds in the United States, he needs to start knocking opponents out, according to his long-time trainer Freddie Roach.

Pacquiao's popularity has declined over the last few years, which Roach attributes to a lack of knockouts and failing to display his killer instinct in the ring. Pacquiao has been without a stoppage win since the fall of 2009, when he stopped Miguel Cotto in the twelfth round.

The Filpino star is scheduled to defend his WBO welterweight title on July 1, against unbeaten 2012 Australian Olympian Jeff Horn (16-0-1, 11 KOs) at the Suncorp Stadium in Brisbane.

Although Pacquiao banked in a monster 4.6 million pay-per-view buys when he faced Floyd Mayweather Jr. in their "Fight of The Century" in May of 2015, his pay-per-view numbers outside of that fight, at least in recent years, have been nothing to brag about.

Part of Pacquiao's decline in popularity, according to most observers, is the selection of opposition. Since getting knocked out by Juan Manuel Marquez in 2012, Pacquiao has faced Brandon Rios, Chris Algieri, Timothy Bradley (twice) and Jessie Vargas. None of those fights were in high demand.

The fight with Horn will be showcased on pay-per-view, and instead will be carried by ESPN.

Roach believes the Pacquiao crowd will return in full force - if the knockouts return.

"I would love to see him get his killer instinct back and go for the knockout. I know we haven’t done that in a long time and the bible has a lot to do with that, and it’s very tough to argue with the bible," Roach told On The Ropes Boxing Radio

"The thing is, people like knockouts in boxing and Manny has lost a lot of his crowd because he hasn’t knocked anyone out in such a long time. I think he needs to get back to that, and I would love to see him do that, and this [bout with Horn] is the perfect fight to do it in."

"The thing is, people get knocked out and they get hurt, this is the game we chose from the beginning. I wish he would just go back to his old self, because he was a really hot product when he was knocking people out. I know he can do it again if I press the right button and get him to fire up."