"I'm coming back to fight Manny Pacquiao this year," Mayweather, 41, said on his Instagram account. "Another 9 figure pay day on the way."
An accompanying video showed the two fighters at a music festival in Tokyo but it was difficult to hear what they were saying.
In a later video obtained by ESPN, Mayweather says, "Tokyo Japan here we go.... I'm coming back in December."
He added, "I'm going to take it (the belt) from him like I did before. We gonna get the payday and I don't want no shoulder excuses."
Ramirez retains WBC title
Undefeated Mayweather scored a unanimous decision that earned him an estimated $220 million. Pacquiao later said he was hampered by a right shoulder injury.
Mayweather was back in the ring in 2017, winning by a technical knockout over mixed martial arts world champion Conor McGregor to run his boxing record to 50-0.
He earned a reported $300 million and McGregor $100 million in one of the richest fights in history.
Pacquiao (60-7-2) last fought in July, knocking out Argentine Lucas Matthysse.
Afterward, when asked about a rematch with Mayweather, the Filipino boxer said, "I have the belt, so it's up to him. If he wants to come back in boxing let's do a second one."
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