Floyd Mayweather has officially offered Irish MMA superstar Conor McGregor $15 million for a crossover bout. Mayweather retired from boxing unbeaten in 2015 with a career record of 49-0 but has said he is willing to come out of retirement for a potential big money showdown with the current UFC lightweight champion.

Mayweather and McGregor rivalry

Mayweather and McGregor's rivalry started with several verbal jabs being exchanged between the two via the media, with both parties showing interest in a potential bout. McGregor, a master of gamesmanship, then obtained his boxing license from the California State Athletic Commission near the end of last year to really get tongues wagging over a potential bout between the two.

However, despite the interest in the match-up, McGregor is currently still under contract with the UFC, making the often strenuous negotiation side of boxing even more difficult to negotiate, but there is no doubt a Mayweather vs McGregor showdown would be extremely lucrative with both men the biggest stars in their sport.

Mayweather makes offer to McGregor

McGregor recently named his price at $100 million to make the crossover out with the five weight boxing champion happen, however, Mayweather offered McGregor a counter deal during his guest appearance on ESPN's "First Take" earlier this week. Mayweather, who turns 40 next month, told the ESPN studio that McGregor had just been "blowing smoke up everybody's ass" stating that McGregor couldn't make such high financial demands to face him considering he had never made "8 or 9 million in a fight" before.

Mayweather, who has said he will only take the bout for a "guaranteed" $100 million then offered the Irishman $15 million for the fight, adding that they could talk about the percentage split of the PPV on top of that.

McGregor is currently taking some time off from MMA to welcome his first child into the world with partner Dee Devlin.

The 28-year old Irishman claimed he wanted to have "a talk" with the new UFC owners before stepping back into the Octagon following his impressive win over Eddie Alvarez at UFC 205. McGregor, who become the UFC's first ever dual champion at UFC 205, has also been in talks with the WWE according to his agent.

Mayweather hasn't fought since defeating Andre Berto in September 2015 in which he retired after the bout.

Other boxers such as Manny Pacquiao, who Mayweather defeated by unanimous decision before the Berto fight, have tried to entice former pound-for-pound king out of retirement on several occasions, however, Mayweather has cited the importance of his health. The boxer had initially claimed that he wanted to end his career 49-0 as a tribute to the great Rocky Marciano, however, a fight with McGregor would change that.