The Up helmer was apparently planning to take on the follow-up as his next project.
However, according to an interview in NY Magazine, the 41-year-old may no longer be attached to the film.
He said: "I'm mostly focused on the next film that I have in development already. That one I just started. We finished Up, I took some time off, spent some time in Europe and Japan doing publicity over there, so I've only been on this for like a couple weeks."
When asked if his next movie is the Monsters, Inc. sequel, Docter replied: "I'm not working on... I'm working on something else, but I cannot announce what it is."
The original 2001 picture featured the voice talents of Billy Crystal and John Goodman.