By Wil Longbottom, News Reporter

It's been built up for months and everyone has their opinion on who will win.

The opening bell in the "Money Fight" between undefeated Floyd Mayweather Jr and Ultimate Fighting Championship (UFC) star Conor McGregor will sound between 4am and 5am on Sunday.

But what exactly can we expect from a spectacle set to generate $600m (£466m)?

Profiles: Mayweather

Image: Mayweather Jr has a 49-0 record leading into this fight

Widely regarded as one of the greatest to pull on boxing gloves, Floyd Mayweather has come out of retirement at the age of 40 for one last fight.


He stands on a perfect 49-0 career record, with 26 knockouts, and if he wins he will move ahead of former heavyweight great Rocky Marciano who has the same current record.

"Money" Mayweather has not tasted defeat since a controversial loss to Bulgarian Serafim Todorov in a semi-final bout at the 1996 Olympics.

He has reportedly earned around $700m (£544m) throughout his distinguished boxing career until his retirement in September 2015 and he has a mansion in Las Vegas, a fleet of exotic cars and a private jet.

Born in Grand Rapids, Michigan, his father Floyd Mayweather Sr once fought Ray Leonard.

While he has been perfect in the ring, outside it he has been accused of assault on at least seven different occasions, including a 2010 incident which resulted in a 90-day prison sentence.

McGregor

Image: Conor McGregor holds two Ultimate Fighting Championship titles

The UFC star is making his debut in the boxing ring after a meteoric rise up through his sport.

Conor McGregor, 29 - who calls himself "Mystic Mac" because of his ability to predict the outcome of his fights - started life training as a boxer before embracing mixed martial arts.

He nearly walked away from the sport of MMA after an early loss as a young professional, but went on to become the first fighter to hold two belts at different weights in the UFC simultaneously.

Mr McGregor, from Dublin, Ireland, recently bought a yacht which he named 188 - after the number of euros he received as a social welfare payment from the Irish government just four years ago.

The fighter has won 21 of his 24 professional MMA fights.

In numbers

Mayweather:

:: 49 - fights - 49 victories

:: 26 - KOs - 53% of fights

:: 26 - world title fights

:: 12 - world titles held

:: 5 - number of different weight divisions he has won a world title in

:: 1 - number of times he has been knocked down

McGregor:

:: 24 - number of MMA fights

:: 0 - number of professional or amateur boxing matches

:: 21 - number of MMA victories

:: 18 - KOs - 75% of fights

:: 13 - number of times he has won inside first round

:: 1 - number of UFC titles he currently holds

What do they say?

Who won the battle of insults?

McGregor: "This is not even close to my toughest challenge ever. I will crumble him.

"I'm a special man, I will prove that August 26, this will go one or two rounds, maybe I will bang him out and hurt him."

Mayweather: "I talked to you before and said that this fight wouldn't go the distance.

"If you're going to bet, bet it won't go (the distance)."

What about the experts?

A champion's gloves: McGregor's home support

Most boxing commentators say Mayweather will win the fight, although they do say that McGregor is a dangerous opponent.

According to SkyBet, the American is 2/9 to win, while his Irish opponent is 7/2 to triumph. The odds of a draw are 40/1.

Rules

McGregor is stepping away from MMA where he has made his name to fight Mayweather in the T-Mobile Arena in Las Vegas.

It will be a 12-round contest under boxing rules, with both fighters using 8 ounce boxing gloves instead of the standard 10 ounce.

That is at the request of Mayweather, who is perhaps hoping his vaunted defensive capabilities will be helped using lighter gloves.

Only punching is allowed, therefore, so no mixed martial arts and no hitting someone if they are knocked to the ground - something which is allowed in MMA.

The event

This fight is threatening to break the pay-per-view record set by Mayweather and Manny Pacquiao two years ago.

Some 50 million people are expected to watch it in the US alone, with the fight available online or on TV screens to more than one billion homes in 200 different countries.

The arena itself is not expect to be full though, with fans having to pay more than $1,000 for a seat.