One of the greatest boxers of all time Bernard Hopkins warned Floyd Mayweather Jr. about being too confident against Andre Berto who will be challenging the unbeaten welterweight champion at the MGM Grand in Las Vegas, Nevada on Sept. 12

The fight, according to Mayweather, will be the last in his storied career as he looks to retire undefeated and tie Rocky Marciano's 49–0 record.

Mayweather said he chose Berto because the 31-year-old boxer is an entertaining fighter and he believes that he will be pushed by the challenger. 

But the majority sees differently as Mayweather is heavily favored to come out of the MGM Grand unchallenged and victorious. 

The 38-year-old undefeated boxer also addressed how the betting for his fight against Berto is going so far and said the gap between him and his challenger should not be that big. 

Despite all of Mayweather's praises to Berto, Hopkins still believes the defending champion will be in danger if he is overlooking his challenger. 

"It ain't what Berto is expected to do or not do, it's what Mayweather do or don't do. Mayweather is now in position to be his worst enemy if he's not taking Berto seriously," Hopkins told Boxing Scene in an interview. 

The 50-year-old added, "The burden is not on Berto, he has nothing to lose. But if Floyd Mayweather is not respecting who he's facing, he becomes more vulnerable."

Mayweather's selection of Berto came as a surprise to many as there are a number of top contenders who were linked to fighting him in his 49th professional bout. 

Names like Amir Khan, Manny Pacquiao, Kell Brook, and Keith Thurman popped out in discussions before Berto was selected. 

Berto has been silent since being given the biggest opportunity in his career, although he said that he will suprise the world and promised a knockout against Mayweather.