Mike Tyson ain't the only heavyweight training for a comeback -- Evander Holyfield tells TMZ Sports he's gearing up for another fight at 57-years-old!
"The Champ is back," Holyfield tells us ... "I’d like to announce that I will be making a comeback to the ring."
Holyfield -- who hasn't had a sanctioned fight in 9 years -- says the goal is to raise money for the #Unite4OurFight campaign which "aims to provide students the resources they need for emotional development and education.