Robert Guerrero is 5-to-1 underdog in Saturday's fight with Floyd Mayweather

Click to enlarge the most recent odds sheet for Saturday's welterweight title fight between Floyd Mayweather and Robert Guerrero.

LAS VEGAS -- Floyd Mayweather remains a heavy favorite ahead of Saturday's welterweight title fight with Robert Guerrero, though the most recent odds at the MGM Grand sports book have reflected moderate action on the lesser-known challenger.

Guerrero is a +500 underdog, meaning a $100 wager returns $500 in winnings. That number is down from +700 when betting opened on Feb. 27.

Mayweather is a -750 favorite, meaning it requires a wager of $750 to win a profit of $100. That number opened at -1100.

A titleholder at 130, 135, 140, 147 and 154 pounds, Mayweather has never lost in 43 professional fights. The 36-year-old from Grand Rapids, Mich., is an odds-on favorite to win by decision (at 5-to-9) with even odds on a knockout.

Guerrero (31-1-1, 18 KOs), who captured world titles at featherweight, junior lightweight and interim belts at lightweight before skipping the 140-pound division altogether to move to welterweight, is 7-to-1 to win by knockout and 11-to-1 to win by decision.

The fight marks Mayweather's first since he signed a six-fight television deal with Showtime and CBS worth a potential $250 million, parting ways with HBO, which had broadcast his previous 23 fights.

-- Bryan Armen Graham