Michael Cera and Alan Arkin may be joining the long, growing list of celebrities playing starring roles and making cameo appearances in Disney’s untitled Muppet movie.  Jason Bobin is directing.

An offer is out to Cera to voice Walter, a living, talking puppet who dreams of one day becoming a Muppet.  In the new, live-action/Muppet hybrid, Walter goes on a quest with his best friend/owner Gary (Jason Segel, who also co-wrote) and Gary’s girlfriend, Mary (Amy Adams), to reunite the Muppets for a big show in order to save the Muppets’ old TV studio from a nefarious oil tycoon (Chris Cooper).

If he accepts the voiceover gig, it would be a new direction for Cera, whose career stokes a new wave of backlash every time he headlines a quirky comedy.  He would also be following fellow Apatow-ites into the voiceover realm, like Seth Rogen (Monsters vs. Aliens, Kung Fu Panda, Horton Heras a Who, Paul), Jay Baruchel (How to Train Your Dragon), Jonah Hill (also HTTYD, Megamind), and Segel (Despicable Me).

According to the latest issue of Production Weekly, Arkin was offered the role of a tour guide at the old Muppets studio.  Arkin was the featured guest on an episode of “The Muppet Show” in 1980 that was later nominated for two Emmys.  Neither Arkin nor Cera are confirmed.

Often referred to as The Greatest Muppet Movie Ever Made and the more humble The Muppets, the cinematic variety show will feature a multitude of famous faces, a throwback to the celebrity appearances in Jim Henson’s “The Muppet Show” in the late ’70s and its marquee movies.  Zach Galifianakis’ involvement was revealed last week and Sean Penn is said to be poking fun at his anger issues in the movie, among other great cameos.

Disney has scheduled The Muppets for Christmas Day 2011.