In the event of a victory, Mayweather, out of his retirement for the event - he has not boxed for two years - will reach the bar of 50 victories, breaking the record of unbeaten Rocky Marciano. If he wins, McGregor will challenge the laws of weightlessness by sending to carpet one of the biggest British boxing charts. The impact would be enormous: you imagine the Olympic champion of the 1 500 m come to beat Usain Bolt in 100 m?