Stoller, who co-wrote the first film, insisted that the new Muppet Walter will be "heavily involved" in the follow-up to the latest movie.
"Walter is coming back," Stoller told New York Magazine.
"Come on, you saw the first one, right? The arc of the story was, 'Am I a man or a Muppet?' Walter chose to be a Muppet. He realised he's a Muppet.
"He is not making a cameo - he is heavily involved in the story."
Segel recently insisted that he has no involvement in the upcoming Muppets sequel.
He previously revealed that he had no ideas on how to continue the story.
Watch Walter singing the Oscar-winning Muppets song 'Man or Muppet' below: