(ABC NEWS) - Floyd Mayweather Jr. says he's coming out of retirement again to fight Manny Pacquiao for a second time in December.

Mayweather posted a video on Instagram early Saturday that showed him and Pacquiao together, reportedly in Japan, jawing at each other over a possible second fight.

"I'm coming back to fight Manny Pacquiao this year," Mayweather said. "Another nine-figure payday on the way."

Whether the fight actually happens remains to be seen. There are no promotional barriers between the two men, because Mayweather promotes himself and Pacquiao is a boxing free agent.

Oddsmakers at the Westgate Las Vegas Superbook immediately made Mayweather a 2-1 favorite.

Mayweather defeated Pacquiao in May 2015 in a massively hyped fight that was largely panned by most boxing fans. The bout delivered a record 4.6 million pay-per-view buys, and Pacquiao blamed an injured shoulder for landing only 81 punches in the fight.

Mayweather, who has won all 50 of his fights, last fought a year ago when he stopped Conor McGregor, the UFC star who was in his first professional boxing match. The 41-year-old Mayweather reportedly made more than $200 million for that fight, on top of a reported $300 million for his win over Pacquiao.

Pacquiao, the Filipino star who will be 40 in December, lost to unheralded Jeff Horn last year before rebounding with a win over Lucas Matthysse in Malaysia last month.

Representatives for the two fighters could not immediately be reached for comment.