McGregor vows to knock out Mayweather at start of media tour

Mixed martial arts star Conor McGregor has vowed to knock Floyd Mayweather out inside four rounds when the pair meet in a Las Vegas boxing match next month.

McGregor has never boxed as an amateur or professionally but will face undefeated former multiple world champion Mayweather at the T-Mobile Arena on August 26 under normal boxing rules.