The 27 year-old Dubliner had been looking into the possibility of a nine-figure clash with Mayweather in September, although a return with Diaz has now been finalized.
McGregor will attempt to rectify a March 5 defeat to Diaz via a rear naked choke hold in the second round after moving up in weight from featherweight.
‘Notorious’ had previously unified the lower limit – at which McGregor has been ruler since 2008 – but now hopes to become a three-division UFC title holder on August 20 at the newly-built T-Mobile Arena in Las Vegas.
— UFC (@ufc) June 5, 2016
Rumours of McGregor under-performing as a boxer in test sparring sessions against the likes of Chris Van Heerden haven’t helped the Mayweather bout get off the ground as many saw the potential fight as wholely one-sided.
Mayweather was looking to face McGregor in a bid to score 50 professional wins without loss and may now turn his attention back to current undefeated WBC welterweight title holder Danny Garcia.
At a Showtime taping earlier this year, Mayweather name-dropped Garcia as a comeback opponent prior to rumours blowing up regarding McGregor.
The 39 year-old pound for pound king retired last September with a routine win over Andre Berto and has already patented TBE 50 and TMT 50 as trademarks in preparation for an imminent ring return.