The untitled computer-animated film is in pre-production at Lucas' Skywalker Ranch production facility in Marin County, California, according to the Hollywood Reporter.
The musical marks a rare step outside the Star Wars universe for the filmmaker, who last directed Star Wars: Episode III - Revenge of the Sith in 2005.
Elf writer David Berenbaum wrote the screenplay, which is tightly under wraps but is rumoured to feature fairies.
Teenage Mutant Ninja Turtles' Kevin Munroe is directing the project, which is expected to feature songs from a variety of sources.
A Lucasfilm spokesperson says it is "too early to comment on the details of the project".
In true straightforward comic-book style TMNT starts with a brief backstory (without the laborious explanation on why four turtles and a rat become human-like in the first place) and then launches into the heart of the movie. After the defeat of their old arch nemesis The Shredder the Turtles—fun-lovin’ Michelangelo (Mikey Kelly) tech guru Donatello (Mitchell Whitfield) hotheaded Raphael (Nolan North) and pragmatic leader Leonardo (James Arnold Taylor)--have grown apart as a family. While Leo is off honing his craft the turtles no longer fight crime--except Raphael who still fights crime under the pseudonym Nightwatcher. Struggling to keep them together is their rat sensei Master Splinter (the late Mako). But strange things are brewing. Tech-industrialist Max Winters (Patrick Stewart) is amassing an army of ancient monsters to apparently take over the world. With the help of old allies April O'Neil (Sarah Michelle Gellar) and Casey Jones (Chris Evans) the Turtles finally come together as brothers to fight the good fight and once again face the mysterious Foot Clan who have put their own ninja skills behind Winters' endeavors. As opposed to hiring just A-list actors TMNT is a nice eclectic mix of veteran voice-over artists who give the Turtles their voices and regular actors such as Gellar Stewart and Evans. Crouching Tiger Hidden Dragon’s Ziyi Zhang also gets in on the action providing the voice of the Foot Clan leader Karai who was once an enemy of the Turtles but now sees the value in what they do. Of course there isn’t a Robin Williams or Ben Stiller to laugh with but Kelly is pretty funny as Michelangelo who has had to resort to entertaining kids at birthday parties as “Cowabunga Carl ” a clown-for-hire in a “fake” turtle suit. It will all depend on whether those ninja-fightin’ pizza-eatin’ giant turtles still have a monetary appeal but methinks a new TMNT movie franchise has been born. The comic book was created in 1984 by Peter Laird and Kevin Eastman as a spoof to the superhero stories and quickly took off into merchandising heaven with a toy license and then a television series. The original 1990 live-action movie used state-of-the-art animatronics but somehow felt static and fake. Since the last TMNT movie in 1993 the whole Turtle phenomenon has sort of fallen off the radar at least in the U.S. so the time was ripe for a renovation. Using the innovative CGI we know and love this new TMNT--created by a team of animators from California and Hong Kong under the watchful direction of Kevin Munroe--gives the Turtles not to mention all the otherworldly monsters they have to fight a realistic look and feel. With this kind of freedom the film can focus on the action which is the best part of the TMNT lore. Though the demographics may skew male ages 8-11 (as well as those 8-to-11-year-old boys who loved it back in the day and are now grown men) TMNT is just your basic supercharged animated fun.