By Edward Chaykovsky

Junior middleweight Tony Harrison (21-0, 18KOs) is only days away from the biggest test of his career, this coming Saturday night in Tampa, Florida against veteran Willie Nelson.

The fight takes place on the undercard to Keith Thurman vs. Luis Collazo. Both fights will be televised as part of the Premier Boxing Champions debut card on ESPN.

Harrison gave his thoughts on another big puncher in WBA/IBO champion Gennady "GGG" Golovkin - and how the middleweight king stacks up against pound-for-pound king Floyd Mayweather Jr.

Golovkin wants to fight Mayweather and he's willing go down to 154-pounds, where Floyd has the WBC/WBA belts. If the fight were to happen, Harrison believes Mayweather would outbox him.

"Floyd Mayweather is just the best fighter in the world and I think he can go up to 154-pounds and beat Gennady as of today. I think he’s a phenomenal fighter, he understands the sport, he understands his craft, he’s mastered his craft," Harrison told On The Ropes Boxing Radio .

"I do think it would be an amazing fight but I think Floyd does what Floyd wants to do, and if he doesn’t want to do that, then he won’t. If he does do it, you always know that if Floyd takes the fight, he believes he can win it. If the fight ever does happen, know that Floyd thinks he can win the fight, and it would make for an amazing fight."