Manny Pacquiao's knockout loss to Juan Manuel Marquez doesn't offer any pointer to how the Filipino great will fare against Floyd Mayweather, trainer Freddie Roach said Thursday.

In the fourth bout of their memorable rivalry, Mexico's Marquez avenged two earlier defeats when he flattened Pacquiao with a hard right in the final second of the sixth round in December of 2012.

Mayweather backers have seized on the fact that over four fights -- Pacman's two victories, a draw and that stunning Marquez KO -- Pacquiao was drawn into gruelling battles against Marquez -- like Mayweather a prolific counter-puncher.

Add to that, Mayweather convincingly out-pointed Marquez in their 2009 meeting.

But Roach said Thursday that the fact that Pacquiao and Marquez had met so many times had given the Mexican an advantage Mayweather won't have.

"Marquez is a great counter-puncher. He fought us four times and learned a lot about us in those four times," Roach said. "He's a smart fighter. He knew what to do when Manny stepped on his foot and lost balance a little bit.

"I wouldn't say he was lucky -- it was well played."

And Roach scoffed at suggestions from the unbeaten Mayweather's camp that the devastating knockout defeat, one of three on his professional resume, had left a permanent mark on Pacquiao.

Even though Pacquiao had to be taken to hospital for evaluation after the bout, Roach knew right away his fighter was OK, because he insisted on washing the blood off his face before boarding an ambulance.

"Manny knows that being knocked out in this sport is part of the sport," Roach said. "If you can't deal with being knocked out, you should find something else."