Transcript for Hype builds for anticipated Mayweather vs. McGregor fight
We move on to this weekend's big showdown in Las Vegas. A live look at the T-Mobile arena where Floyd Mayweather is going to take on ufc champion Conor McGregor tomorrow night. The payoff is huge, the hype couldn't be higher and T.J. Holmes has the story. Good morning, George. These are absolutely the two biggest stars in fighting and they arguably have the biggest mouths and the biggest personals but that translates into them being big draws and that means big money. This is expected to be the most watched pay-per-view fight in history but why now a group of concerned doctors say it should not be taking place? Reporter: 50 million are expected to watch this weekend's highly anticipated much hyped sports spectacle. In one corner the outspoken Irish star of the ufc Conor McGregor. I mean I'm not only am I going to beat him I'm going to beat him under the specific rules that he has -- that favor him. Reporter: A mixed martial artist heralded for his ability to wrestle and throw elbows. In the other corner a guy who's only thrown punches Floyd Mayweather at 49-0 considered the greatest boxer of his generation. Get it right now. You can get it right now. Reporter: The fight could bring in as much as $700 million. But many in the medical community question whether the fight should even be taking place. Thou McGregor is a mixed martial arts star this will be his first professional boxing match and this morning more than 100 ringside doctors are expressing surprise the fight was even sanctioned in the first place citing fears someone could get seriously hurt by putting a boxing novice in the ring against an all-time great boxer. This past June Tim haig died after he sustained injuries in a boxing match. It was only his fourth. In the end money talks and the fight between Mayweather and McGregor, the two biggest stars in combat sports will undoubtedly be one of the biggest cash cows in sports history. So who you got? This is not a good guy versus bad guy situation. This is bad guy/bad guy. Rich guy/rich guy. McGregor is flat out accused of racism in some of the promotion. Floyd Mayweather with that history of domestic violence so bad guy versus bad guy. A lot tell you we are being conned. This should not be taking place. It is not competitive. You can't talk too much about it because we'll wake up Sunday morning and McGregor knocks him out in one punch but the chance of that happening. One of the greatest boxers in history has been doing this his whole life going up against a guy who's never had a professional fight. That's silly to be honest with you but these are two big guy, big draw. All about money and have this money belt even, look at this thing, they came up with. Not fighting for a real belt. They got dimes and rubies and throwing cash -- I don't even know how much this thing is worth but this is just -- it's gratuitous, all right, 220 million is what he made for the Pacquiao fight. He's expected to make at least that or maybe more. Because people are watching. I dot to buy this thing this weekend. We're suckers. A lot will be watching. We'll watch "Nightline" tonight as well. Conor McGregor's interview will be on "Nightline."
This transcript has been automatically generated and may not be 100% accurate.