In a posting on the MMA website, the 40-year-old American said he wants to face McGregor, 28, in June.
«For Conor McGregor, I’m coming out of retirement, just to fight Conor McGregor,» Mayweather told FightHype, according to the posting.
«Today, I’m officially out of retirement for Conor McGregor. We don’t need to waste no time. We need to make this… happen quickly. Let’s get it on in June.»
Mayweather had matched Rocky Marciano’s iconic 49-0 unbeaten career record when he walked away from boxing as the welterweight champion in 2015.
Speculation of a Mayweather-McGregor fight has intensified in recent months, with the US star saying he is willing to meet McGregor in a boxing ring.