Updated

By Kieran Mulvaney

LAS VEGAS (Reuters) - WBA welterweight champion Shane Mosley is unconcerned about being labeled an underdog for Saturday's fight against Floyd Mayweather Jr. in Las Vegas, believing he will knock out his opponent.

Mayweather, renowned as a superlative defensive fighter, has never been knocked down or defeated and is a strong favorite to record his 41st victory on Saturday but Mosley believes he can shock the world and deliver a stoppage win.

Mosley, 46-5 (39 knockouts), however, has not fought since a ninth-round TKO upset of feared Mexican slugger Antonio Margarito in January 2009.

"I really don't care," the 38-year-old champion told reporters on Wednesday about the underdog tag.

"They were picking Margarito to win by landslide, and people were worried about my health and saying he was going to retire me.

"I'm saying to you guys again, that isn't going to happen. He's not going to beat me."

Mayweather retired as the sport's pound-for-pound number one fighter after beating Ricky Hatton in December 2007 but returned in style in September, outclassing Mexican Juan Manuel Marquez over 12 rounds.

He had been expected to fight Filipino Manny Pacquiao but the pair could not agree to a drug testing procedure leading to Mayweather agreeing to take on Mosley, which the champion believes could be a mistake.

"Fighting me can be hazardous," Mosley said. "The times I have knocked out people, a lot of the fighters don't come back the same.

Mosley acknowledged that it would be "shocking" to see his opponent lying on the canvas but it was something he would look forward to witnessing.

"I go for a knockout, but I'll be shocked to see him just laying there on his back like that," he admitted. "Happy, but shocked."

"When the fight starts, I'm going to go out there, I'm going to throw some traps here and there, touch him here and there, see what's going on," he revealed. "I'll probably be able to tell from the first bell what kind of fight it's going to be."

Although Mayweather, 40-0 (25 KOs), has won most of his bouts with relative ease, some observers have pointed to his split decision win over Oscar De La Hoya in May 2007 as providing the blueprint to defeating him.

De La Hoya troubled Mayweather in the first half of the contest with a stiff left jab, a punch that Mosley agreed could be a key on Saturday.

"It's been proven," he said. "Not just Oscar, but other fighters. Some of the southpaws fought him pretty good with their left hands. So maybe it's not a jab, maybe it's just a left hand.

"But that's just one strategy. I can't just base my fight on throwing a jab. You have to be ready for a bunch of different things, because you're fighting a special fighter."

(Edited by Patrick Johnston)