While the possible #UFC vs. boxing match-up will no doubt be a historic affair that brings in millions of eyeballs, it won't have the honor of being the first cross-sports battle. Over the decades, fans have witnessed a slew of super fights, freak show bouts, and other beat downs that somehow were sanctioned by athletic commissions.
Below, here's a history of notable combat sports fights that we can't believe actually happened.
Muhammad Ali vs. Antonio Inoki
Long before the rise of mixed martial arts, the legendary Muhammad Ali tested his boxing skills in a martial art vs. martial art bout against Japanese pro wrestler Antonio Inoki in 1976.
While there was a ton of anticipation leading up to the fight, the actual battle proved to be an embarrassing affair for both combatants. Trying to capitalize on the match's special rules, Inoki spent nearly the entire fight on his back, attempting to kick Ali's legs from the ground. As for Ali, "The Greatest" only threw six punches in the bout, which ended in a draw.
Although fans weren't exactly happy with what transpired, the battle served as a high profile precursor to the sport of #MMA.
Royce Gracie vs Akebono
Having dominated the competition during the early days of the UFC, Brazilian Jiu Jitsu pioneer Royce Gracie is no stranger to crazy match-ups against larger opponents.
While there are plenty of freak show bouts to choose from Gracie's long career, one of his most head scratching fights came against former sumo wrestler Akebono Taro at a 2004 K-1 event. Held under MMA rules, Gracie had little trouble against his towering foe, scoring an omoplata just over 2 minutes into the first round. Once again, the legendary former UFC champ proved that technique beats size nearly every time.
Butterbean vs. Bart Gunn
Affectionately known as Butterbean to hardcore fans, Eric Esch has tried his hand at several combat sports over the years, including boxing, kickboxing, and MMA. One of his most memorable victories, though, came inside the WWF ring.
During the promotion's short-lived attempt at putting on legitimate shootfights, Butterbean got a chance to take on the WWF's one and only Brawl for All tournament champion Bart Gunn. Butterbean came out of their 1999 WrestleMania XV match victories, knocking Gunn out in just 35 seconds.
CM Punk vs. Mickey Gall
Unless your name is Brock Lesnar, most #WWE stars haven't fared well inside the Octagon. Just ask CM Punk.
The former pro wrestler finally made his UFC debut in 2016, but the results were less than stellar. Taking on the very green MMA rookie Mickey Gall, CM Punk was dominated in his match-up at UFC 203. Unable to even land a punch, the ex-WWE fighter eventually tapped out to a rear-naked choke early in the first round.
The fight was a prime example as to why you should only step into the cage if you're an actual martial artist, not just a person who pretends to be one on TV.
Jose Canseco vs Hong-Man Choi
Infamous ex-MLB star Jose Canseco got more than he bargained for when he took on Hong-Man Choi at Dream 9 in 2009.
Canseco's night didn't last long as Choi made quick work of the former baseball player, tapping him out with strikes just over a minute into the first round during the Super Hulk Grand Prix. Going out on a limb here, but if Canseco ever gets his wish of having a fight against Shaquille O'Neal, we're guessing the results will be pretty similar.
Mariusz Pudzianowski vs. Bob Sapp
Perpetual tomato can Bob Sapp probably has more strange fights on his record than any other combat sports star in history.
Aside from losing to pro wrestlers and MMA fighters, Sapp also has a defeat on his record to the "World's Strongest Man," Mariusz Pudzianowski. The pair faced off at an event in Poland in 2012, and it only took Pudzianowski 40 seconds to finish Sapp with knees and punches.
Lawrence Taylor vs. Bam Bam Bigelow
1995's WrestleMania XI featured a peculiar main event battle between former NFL linebacker Lawrence Taylor and Bam Bam Bigelow.
The odd match-up came about following a war of words at that year's Royal Rumble, and has since become one of the most controversial fights in the promotion's history. While fans were torn over a football player getting a shot in the ring, the match brought in a ton of mainstream coverage and has even been credited with saving the WWF.
Taylor, along with a ton of his NFL pals, would go on to win his battle with Bigelow, who was subsequently kicked out of Ted DiBiase's Million Dollar Corporation after the loss.
Randy Couture vs. James Toney
Preceding the McGregor-Mayweather mayhem, the UFC and boxing first came to major blows at UFC 118 in Boston.
Former champ Randy Couture showed the combat sports world why MMA has an advantage over the sweet science inside the Octagon, easily taking Toney down before securing an arm-triangle choke in round one. Sadly, the pugilist was unable to put an attack together, serving as a very expensive grappling dummy for "The Natural."
Gabi Garcia vs. Yumiko Hotta
BJJ ace Gabi Garcia is a scary competitor to face, no matter who you are.
The Brazilian bruiser offered 50-year-old pro wrestler Yumiko Hotta no mercy in their #Rizin fight on New Year's Eve. Garcia demolished Hotta, easily finishing her via TKO in the first round.
Only in Japan will you see a middle-aged woman get pummeled by heavyweight BJJ black belt.
Tim Sylvia vs Ray Mercer
Prior to James Toney's fiasco in the cage, former boxer Ray Mercer thought he could hang with a mixed martial artist, and he was right.
Mercer quickly showed former UFC champ Tim Sylvia why you shouldn't eat a punch from a pro pugilist during their 2009 match. It only took Mercer nine seconds to turn Sylvia's lights out with a vicious overhand right.
Floyd Mayweather Jr. vs. Big Show
Mayweather will never set foot inside the Octagon, even if he does book a match against McGregor. However, he does have a history inside the WWE ring.
The boxer had a showdown with Big Show following their spat at a 2008 PPV event. The pair eventually squared off in a one-on-one, no DQ match at WrestleMania XXIV, which resulted in another win on Mayweather's record. Using brass knuckles, Mayweather KO'd Big Show in what would be a very lucrative night for the undefeated pugilist as well as the wrestling promotion.
Mirko Cro Cop vs. Alberto Del Rio
When will WWE guys learn? Don't step inside a ring or cage against MMA fighters. Alberto Del Rio learned this lesson the hard way against UFC and kickboxing vet Mirko Cro Cop.
Going by the moniker Dos Caras Jr. at the time, Del Rio stepped into the ring donning a luchador mask against Cro Cop during their 2003 fight at Pride Bushido 1. The colorful attire didn't do much to help, though, as Cro Cop obliterated Del Rio with a head kick 46 seconds into round one.
Minowaman vs. Giant Silva
One of the few Silvas to match the size of Bigfoot Silva, Paulo César da Silva, aka Giant Silva, was a towering figure during MMA's earlier days. The former Brazilian basketball player didn't exactly have a great run in MMA, though, amassing just a 2-6 record during his career.
However, one of his more entertaining match-ups came against Ikuhisa Minowa at Pride Bushido 10 in 2006. Unfazed by the massive size difference, "Minowaman" miraculously secured a takedown before finishing Silva with strikes in the first round. There's a reason why the Japanese legend is called "The Giant Killer."
Kimbo Slice vs. Dada 5000
Street brawler turned MMA icon #KimboSlice made a career out of taking on crazy fights, but his strangest bout would sadly be his last.
The late fighter passed away just a few months after his hard to watch battle against Dada 5000, another online star and street fighter, at Bellator 149. Both men were insanely out of shape for the match-up, and Dada 5000 even had to be rushed to the hospital following a health scare in the third frame. The bout would only be outshined by the absurdity which was the Ken Shamrock vs. Royce Gracie main event.