By Edward Chaykovsky

Legendary Hall of Famer Sugar Ray Leonard knows what it's like to be the underdog, moving up in weight for a dangerous fight.

In April of 1987, Leonard returned to the ring after a three year layoff, and moved up by two weight divisions, to face the dangerous and some felt unstoppable, middleweight king Marvin Hagler, who had gone undefeated since 1976.

Leonard was a huge underdog, but he defied the odds and managed to pull off a split decision win in one of the most memorable bouts in boxing history.

On September 10th at the O2 Arena in London, IBF welterweight champion Kell Brook (36-0, 25KOs) will attempt to pull off the same feat - when jumps up by two weight divisions to challenge Gennady 'GGG' Golovkin (35-0, 32KOs) for the WBA, IBO, IBF, WBC middleweight titles.

Brook, like Leonard, is a huge underdog in the contest and given little chance to pull off an upset.

"The general consensus is that he does not have a chance, he can't win, but he has to believe in himself," said Leonard to Sky Sports. "For me, I fought at my best when I was the underdog. I was more focused and determined. For Brook, if he feels the same way, that is a plus.

"He also has to be in the best shape ever, capital E, to maintain the tempo and the pace of Golovkin. He has to be mobile, in and out, and try to confuse triple-G. He has to do what he does best and be himself, but faster, quicker, smarter, more economical."

"To maintain the weight was quite difficult, I was kind of a natural welterweight. My weight would not go beyond 155 so it was very difficult trying to maintain 160. I was trying to figure out what weight I should be. As the fight got closer, I weighed in at 158, which didn't take away from my speed and didn't take away from my mobility.

"Brook has to understand what weight is he most comfortable at, what weight won't take away his speed or his movement. I kept moving, I could not stand toe-to-toe with Marvin Hagler. The times I did, was just to release my combinations, and then get back out. I could not be a stationary target because it wears you down against a bigger guy, a heavier opponent."