Michael Bay -- Leonardo AND April O'Neal Have My Back!

Michaelangelo needs to back the hell off of Michael Bay and let the guy turn the Teenage Mutant Ninja Turtles into aliens ... this according to the guy who voiced Leonardo.

TMZ broke the story ... Bay has been getting some serious flack ever since he announced he'll be changing the classic TMNT sewer-based origin story for his upcoming live-action flick.

But not every member of TMNT-nation is hating on Bay's idea to go intergalactic with the Turtles ... in fact, TWO former actors who starred in the original live-action movie are coming to Bay's defense.

TMZ spoke with Brian Tochi -- the original voice of Leo AND the Asian geek Takashi in "Revenge of the Nerds" -- who tells us, "If Michael Bay wants to do a different take on the turtles origin story ... Mazel Tov!"

We also spoke with Judith Hoag -- aka April O'Neal in the classic Turtles flick -- who says she's excited about Bay's new vision ... but her opinion might be slightly slanted.

"I was in "Armageddon" ... which Michael directed ... as well as "Nightmare On Elm Street" and "I Am Number Four" which he produced."