The UFC star will take part in his first boxing fight at either amatuer or professional level against the undefeated multiple world champion at the T-Mobile Arena on August 26.
Mayweather is considered one of the best boxers of all time pound for pound, but McGregor is confident that he can pull off an upset and ruin the 40-year-old's perfect 49-0 record.
"I am honoured to be here, to give you this spectacle. His little legs, his little core, his little head, I am going to knock him out inside four rounds, mark my words," he told reporters at a press conference.
"I am a young, confident, happy man that has worked extremely hard for this. I am just up here embracing everything. No-one can do anything to me. I am just enjoying myself and having a good time.
"He will be unconsciousness in four rounds. He has never faced this. I don't fear him. All these rules, all these restrictions, it doesn't faze me; it amuses me. It is funny to me all these rules. All I need is a gum shield. Line me up to the ring and I am good to go."
McGregor is the only UFC fighter to hold a world title in two different weight divisions.