More than a decade ago, Irish welterweight Dean Byrne had trained at Freddie Roach's Wild Card Boxing Club, located in Los Angeles, California.

And Roach used him as a key player in Manny Pacquiao's training camps for important pay-per-view fights.

He was used as a sparring partner for three of Pacquiao's fights with Juan Manuel Marquez, and the breakout clash with Oscar De La Hoya.

During the period when Byrne made his bones at the Wild Card, Roach started training a once-beaten British star in Amir Khan, who was looking to rebuild his career after being blown away by Breidis Prescott in one round.

Roach also used Byrne as a sparring partner for Khan.

Roach would often have Pacquiao and Khan spar in camp - as they usually had fights coming up in close proximity on the schedule.

In numerous interviews, Roach revealed that Pacquiao had often decked Khan and even knocked him out in sparring.

Byrne was not personally present for the incident, but others in the gym had informed him that Pacquiao knocked Khan out cold during a sparring match. 

"I didn't see it myself," Byrne said to Sky Sports. "Khan was all over the place on many occasions and everybody at the gym knows it. I heard stories that he was asleep on the floor. I have heard that.

"Khan's chin is just like that. He is a great fighter, a great athlete, a super boxer, his hand speed is so fast. But his chin? He hasn't got a good chin. You can't put muscles on your chin. Freddie wanted him to get in, get out, get in, get out. But Khan stays in the pocket for too long to please the crowd, then he comes unstuck because of his chin."

Khan eventually parted ways with Roach in 2012. Pacquiao is still trained by the Hall of Fame coach.

The Bolton boxer has often called for a fight with Pacquiao - and in 2017 they were very close to deal to fight in the Middle East.

Byrne, who had the opportunity to spar both many times, would confidently back Pacquiao to knock Khan out.

"Pacquiao would have knocked him out back then, yesterday, today or tomorrow. Pacquiao would knock him out forever," Byrne said.

"Khan is much faster than Pacquiao. But the power that Pacquiao poses? There is nothing in Khan's punches. When Pacquiao hits you, you know it.

"It's like a cap gun when Khan hits but it's like a machine gun when Pacquiao hits."