Floyd Mayweather 'Coming Out of Retirement' in 2020, Working with UFC

Floyd Mayweather says he's COMING BACK -- insisting he'll fight once again in 2020 ... and working with UFC's Dana White to make it happen.

"Coming out of retirement in 2020," 42-year-old Mayweather posted on social media late Thursday night.

Floyd also posted a pic with Dana White and said the two are "working together again to bring the world another spectacular event in 2020. #boxing #UFC #mma #mayweatherpromotions."

Of course, Floyd and Dana sat next to each other at the Clippers vs. Celtics game in L.A. on Nov. 20 and were seen chatting it up.

So, will it be a boxing match or an MMA fight? We're working on the details.

Floyd has floated a bunch of possibilities over the years -- saying he'll fight everyone from Khabib Nurmagomedov to a rematch with Conor McGregor.

Back in 2018, Floyd said he was definitely fighting Khabib and told TMZ Sports he'd made 9 figures for the fight.

Since then, Khabib's manager Ali Abdelaziz has told us Floyd's camp has been hounding him with calls trying to get the deal done.

There have also been rumblings that Floyd is trying to set up a rematch with Manny Pacquiao, who's looked AWESOME in his last few fights ... even beating Keith Thurman.