Manny Pacquiao -- Unretires from Singing ... Records New Song for Mayweather Fight

Just one month after he swore off singing forever, Manny Pacquiao has pulled a Jay Z -- UNRETIRING from music ... to record a brand new song the Floyd Mayweather fight!

Manny hit the studio recently (according GMA News in the Philippines) and laid down the tracks for "Lalaban Ako Para sa Pilipino" ... which we're told translates to "I Fight for Filipinos."

Our Filipino translators tell us Manny recorded to song specifically for his entrance music for the May 2nd superfight in Vegas.

It's an interesting move ... since Manny appeared on "TMZ Hollywood Sports" last month and told us he stopped singing forever because, "I love music ... but I don't think music loves me."

#ChangeOfHeart