Mayweather retired for a third and final time after defeating McGregor in August 2017 but his latest Instagram post suggests a comeback may be on the cards.
Freddie Roach claimed Manny Pacquiao's entire team was prepared to see him in the ring against Floyd Mayweather for another flight.
Mayweather beat Pacquiao by unanimous decision when the two collided in a much-anticipated fight in May 2015.
The boxing legend finally met his match when going up against "Bone Collector" Larry Williams in a charity basketball game.
Surprise bout is scheduled for December 31 at the Saitama Super Arena, just outside Tokyo.
Anthony Joshua could earn as much as $50 million per fight if he switches to MMA.
"Money" Mayweather improved to 50-0 with his win over the MMA champion.
By the eighth round, the most feared man in the UFC was scuffling with all the ferocity and accuracy of a middle manager arguing with a colleague at after-work cocktails.
The two celebrities are showcasing racism, oppression and hatred in all their forms.
In the space of less than a week, Conor McGregor and Floyd Mayweather have thrown mostly everything at each other except physical objects and their fists.
The two men traded insults in Los Angeles ahead of their fight on August 26.
The Filipino boxer enters the ring on Saturday, against Australian Jeff Horn.
The Irishman is known for his showmanship outside the ring.
The Canadian died on Sunday having fallen into a coma.
The pair will meet in Las Vegas on August 26.
McGregor will switch sports to take Mayweather on at boxing.
The UFC president will speak to the McGregor camp on Sunday.
Hardy was the first Briton to fight for a UFC title.
McGregor believes the campaigners have the wrong mindset.