Hall of Fame trainer Freddie Roach is convinced that his boxer, Manny Pacquiao, would have come away victorious in the fight with Floyd Mayweather Jr. - if Pacquiao's shoulder was 100%.

In the most financially successful fight in boxing history, Mayweather won a twelve round unanimous decision over Pacquiao in May 2015 at the MGM Grand in Las Vegas.

Pacquiao has long claimed that he entered that fight with a pre-existing shoulder injury and then further injured that area during the fourth round of the fight.

To this day, Pacquiao maintains that he did enough to beat Mayweather on the cards - but also says his shoulder gave him trouble during the contest and affected his performance. Pacquiao underwent surgery a few days later.

 A rematch never happened, because Mayweather retired in September 2015.

"A lot of people thought that Manny won the first one anyways, and I think if he didn’t have a bad shoulder at that time, I think we would have. That’s the fight game, how many times do you go into a fight being 100% healthy? Almost never, getting ready for fights is very difficult," Roach told On The Ropes Boxing Radio.

Unlike his career rival, Pacquiao - at 38-years-old, has continued to press forward with his career. He briefly retired last April and then came back in the fall to defeat Jessie Vargas for the WBO welterweight championship.

Roach believes his fighter is still training as hard as ever. Pacquiao is scheduled to make a defense of his title on July 1, when he faces unbeaten Australian Olympian Jeff Horn at Suncorp Stadium in Brisbane.

"He’s still very good, his work ethic is great. He works hard for every fight, he doesn’t take anyone lightly and he works really hard. His work ethic is still like it was the first day I met him. We’re going to go out there and I think demolish this guy, which is what we need to do," Roach said.