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Many factors favor Keith Thurman, right, getting a shot at Floyd Mayweather.

(AP Photo)

LAS VEGAS — Floyd Mayweather knows who he fights this week but the list of potential opponents for a second fight in 2014 got shorter Thursday when Amir Khan said he wouldn't fight in September on religious principle.

Keith Thurman said he'll fill the breach.

If Mayweather beats Marcos Maidana in their welterweight unification Saturday, he would add the World Boxing Association title to the World Boxing Council title one he already has. Mayweather also has WBA and WBC titles at super welterweight (154 pounds).

A victory Saturday also means Mayweather would inherit Thurman as his WBA mandatory challenger at 147 pounds.

Thurman has been the WBA's No. 1-ranked welterweight contender since Aug. 3, 2013, so by the time the Mayweather-Maidana winner could fight again, that winner would be obligated to fight Thurman, unless exempted by the sanctioning body.

Of course, with four titles and two sanctioning bodies to satisfy, the likelihood is small that Mayweather can meet his annual mandate to defend against all of his No. 1-ranked contenders.

"Floyd calls the shots," Thurman said. "Floyd picked this fight here. The one way I see Floyd fighting me (is via the mandatory)."

Thurman (23-0, 21 KOs) is coming off a third-round demolition of Julio Diaz last Saturday at Home Depot in Carson, Calif., and has fought exclusively in stadiums and major arenas since 2010.

He has held the interim WBA title since July 2013 — Mayweather said this week that interim belts should be abolished as part of any effort to clean up boxing — and is due his title shot, by rule.

"I'm a young, up-and-coming, rising star," Thurman said Thursday. "I have yet to fight any world champion. A lot of them claim they have many reasons not to fight me. And it would be nice to give Floyd a reason to fight me. So we'll see what happens."

So why would Mayweather consider fighting the 25-year-old native of Clearwater, Fla.?

One, both are advised by Al Haymon, whose long-standing tendency to keep his fighters from facing each other has been broken recently, including in Mayweather-Maidana.

Two, while both have fought extensively under Golden Boy Promotions' banner, neither is contractually bound to the company. With Golden Boy going through a potential shakeup with the possibility of CEO Richard Schaefer's departure after this fight — possibly to align himself corporately with Haymon and/or Mayweather -- that could make a smooth negotiation for if Mayweather's next fight is exclusively self-promoted or promoted by both Mayweather Promotions and another company.

Three, if a 37-year-old legend like Mayweather is to take on a 25-year-old lion like the heavy-handed Thurman, who has been professional since 2007, the sooner the better.

"I've been 18 years in the game, solid, since the amateurs, and I feel ready," Thurman said. "Would I be more ready a year for now? That's an argument to bring up. But I feel ready today. So we'll see what happens tomorrow."

Thurman said he "most definitely" would like to fight Mayweather next.

"I love a challenge," Thurman said. "I don't really see anybody as a greater challenge than Floyd Mayweather but I don't count myself out. I'm not going to be there just looking for a payday. I'm also trying to make history with my career."

In truth, it would not be surprising if Mayweather doesn't know the identities of all the mandatory challengers he already has, even before potentially adding Thurman to the list with a win Saturday.

At 154 pounds, the WBA No. 1 slot is vacant, while the WBC's top contender is Sergey Rabchenko of Belarus.

At 147, the WBC No. 1 contender is Luis Carlos Abregu of Argentina, with Khan at No. 2.

If Khan defeats Luis Collazo on Saturday, he potentially could leapfrog Abregu. That could allow Mayweather to retain at least one title into 2015 without satisfying his mandatory this year, based on Khan declining an offer for a September fight on religious principle. It also would give the WBC justification for not stripping everyone's biggest cash cow, Mayweather.

The WBA, meantime, has only three No. 1-ranked contenders who have held those positions longer than Thurman.

Super middleweight Stanyslav Kashtanov broke into the November 2012 ratings and has awaited champion Andre Ward, boxing's consensus No. 2 pound-for-pound behind Mayweather, ever since. Lightweight Yuriorkis Gamboa of Cuba has been top-ranked since the June 2013 ratings, with countryman Richard Abril the champion throughout that time. Light flyweight Albero Rossel of Peru has been top-ranked since the April 2012 ratings, with his freeze likely to end after that title recently was vacated.

The next-longest uninterrupted wait by a WBA top-ranked contender is Thurman's.

That's due to end regardless who wins Mayweather-Maidana.

"I'm one of the most-avoided fighters. He's supposed to be the best ever," Thurman said of Mayweather. "So why not take the best ever and fight against the young, rising star who is the most-avoided welterweight and one of the most-avoided fighters in the game of boxing today?"

Mayweather-Maidana: Floyd trains for May 3 fight 38 Gallery: Mayweather-Maidana: Floyd trains for May 3 fight

— David Mayo has covered Floyd Mayweather throughout the fighter's career. Contact him at dmayo@mlive.com.