In an interview with The LAD Bible, McGregor says Mayweather is afraid to fight (at 10m50s in video).
Floyd’s afraid of a fight. Floyd doesn’t want the fight. Floyd wants a boxing match. And I’ve already said ‘No problem! Get my f-cking money. And when you get my money then we can box, in this boxing match, under this set of specific rules that will keep you alive. I’m here. Where’s my money? Cos If you keep dropping my name and you don’t have the money I’ll show up at your front door, so we’ll see…I don’t need rules, so I’m open. Right now it’s just talk.