Since Conor McGregor was pulled from the UFC 200 card, questions have lingered over his next opponent. A UFC featherweight title match against Frankie Edgar or Jose Aldo are considered options, as well as a return to 170 pounds for a rematch with Nate Diaz. But one potential opponent grabbing recent headlines should essentially be ruled out: boxer Floyd Mayweather Jr.

A seemingly implausible "rumor" gained traction Friday that Mayweather and McGregor were close to finalizing a boxing fight. The speculation not only hasn't dissipated but actually seems to be picking up steam, with multiple media outlets adding credence to what amounts to a fantasy fight. It would be unprecedented for a veteran boxing champion to fight a UFC fighter with zero professional boxing experience.

British tabloid  The Sun reported that sources claimed the two sides were "on the verge of agreeing" to a fight, and an agreement on the purse is "imminent." It also stated that Mayweather would make $144 million, and McGregor would take in $10 million. 

Mayweather, never one to shy away from causing a stir, claimed responsibility for the rumor over the weekend.

"It's possible. It's possible. There was a name that was shot at me. But the rumors that y'all have been hearing [are] the rumors I started," Mayweather said, via "It may not be a rumor. Keep your fingers crossed. It may be a boxer versus an MMA fighter. So we just don't know."

McGregor, who reportedly won the Irish Amateur National Boxing Champion title but has no professional record, fueled the fire when he shared a poster for a potential fight between himself and Mayweather on social media. It shouldn't be surprising for either Mayweather or McGregor to promote a fight that isn't confirmed, especially McGregor, who recently said he had a rematch with Diaz lined up despite UFC president Dana White's claims to the contrary.

Mayweather, who is president of Mayweather Promotions, seems to want to return to fighting despite being nine months removed from competition. Seeking his 50th win, the 39-year-old may only want to risk his undefeated record for a purse that nears the record sum he received in 2015 when he fought Manny Pacquiao. But there are no welterweight boxers capable of guaranteeing that type of payday, other than the Filipino star, and Mayweather almost certainly knows it. 

Meanwhile, McGregor currently doesn't have an upcoming opponent, despite being UFC's most recognizable male star. A bout against Mayweather would thrust McGregor's profile into another stratosphere, but there are consequences. A big payday for McGregor, who is coming off a loss to Diaz, may also mean accepting an almost certain defeat to Mayweather, who should have an easy time with an inexperienced boxer.

Setting aside the fact that boxing and MMA are two different sports, the fight likely wouldn’t be allowed to take place no matter how much Mayweather and McGregor want it. White told “The Dan Patrick Show” on Wednesday that Mayweather can call him if he wants to fight McGregor, but the logistics buried beneath the mammoth hype make the proposed boxing match nothing more than a pipe dream.

"It's not true; it's just a tabloid story," White told Yahoo Sports last week about a potential Mayweather-McGregor fight. "And as far as I knew, Floyd is retired and he's been on a world-wide vacation and hasn't even been thinking of fighting."

McGregor’s contract almost certainly doesn’t allow him to fight outside of UFC, and even if UFC could find a way to profit off such a bout, White likely wouldn’t risk his No.1 draw getting injured in a boxing match. Also, it's unclear if the Nevada State Athletic Commission would even sanction the fight, which is important since Mayweather hasn't fought outside of Las Vegas in over a decade.

International Business Times reached out to Bob Bennett, executive director of the NSAC, but did not receive a response, and an administrative assistant at the Irish Amateur Boxing Association could not confirm McGregor's amateur boxing record.

The possibility of McGregor jumping to boxing while he's still a UFC fighter might be the biggest roadblock to this improbable bout. When Ronda Rousey, UFC's most popular female fighter, appeared at WrestleMania 31 amid speculation she might do even more with WWE, White indicated he wouldn’t let a top pay-per-view draw like her compete in a scripted wrestling match. It’s hard to believe he would allow McGregor to make his professional boxing debut against the most accomplished boxer in decades.

McGregor isn't the first UFC fighter to attempt to fight outside of UFC. Eight years ago, then-UFC heavyweight champion Randy Couture tried to break his contract and fight Fedor Emelianenko, who was fighting for Affliction, another MMA promotion. But the fight never materialized, and it's hard to imagine White allowing it now or in the future.

Moreover, such a highly lucrative bout would also mean lengthy negotiations that could stall McGregor's career. Before Mayweather finally fought Pacquiao, talks dragged for years with both boxers aware of the gigantic payday that awaited them. In the mean time, both boxers had the luxury to keep fighting other boxers. Because he is contracted with UFC, McGregor could risk missing out on MMA fights while lawyers iron out details of an unprecedented event outside UFC.

If McGregor wants to fight the fickle Mayweather, it has to happen soon. Already coming off his first loss in UFC, another UFC defeat would drastically damage the value of the hypothetical super-fight. Waiting for a boxing event that would be tangled up in negotiations, McGregor could be forced to drop his featherweight title and damage his UFC options.

The prospect of Mayweather and McGregor fighting is understandably an exciting one for the general public. While there are aspects of boxing in MMA, it’s not a realistic possibility for McGregor to compete with Mayweather in the squared circle. McGregor’s self-confidence is second-to-none, but he must know that he would have no chance against a boxer who has defeated some of the best boxers of the last two decades. A fight with Mayweather would almost certainly give McGregor the biggest one-day payday of his career, but it would also likely mean a severe hit to his fighting reputation, something that McGregor appears to highly covet. 

The heavy media attention for the bout has prompted odds makers to take notice, with setting a betting line. Mayweather was made a -2000 favorite, and McGregor was given +900 betting odds.