"I don't think I have seen a Muppet on set. (This time) they were filming in London and I was in the studio the whole time. So I work with them in the studio but never on set," he told Collider.
Bret teased that Miss Piggy will perform an "exciting" duet in the sequel, "Muppets Most Wanted", but remained tight-lipped about her singing partner. He also revealed that Ricky Gervais will sing with a frog, hinting it could be Kermit's evil doppelganger Constantine.
"Piggy does a ballad. I can't say much more about it, but it's exciting," continued the New Zealand singer-actor.
"Ricky Gervais does a song with a green frog - it might or may not be Kermit. He's got a really good singing voice so that was cool. It's always more fun when the actors come in and they can really sing, like Jason Segel."
Bret - who next stars in Austenland alongside Keri Russell- admitted to feeling some pressure to top the original since winning the Oscar.
"It's hard not to have that pop up in your mind every so often, and obviously, it's not a very helpful thought in the creative process because you don't want to be judging yourself as you go. It's hard not to compare to the last one, which is the problem with sequels," he said.