The 30 Rock star has stepped away from the Adam Shankman musical for unknown reasons, just as filming is set to start.
Jesse Eisenberg is also in talks for a lead role in this upcoming comedy, which will be shot in Rome.
Actor Alec Baldwin said his and Tina Fey's contracts expire in 2012, and they will both be moving away from this hit NBC comedy.
The 30 Rock star was set to play the boss of MIB in 1969, although scheduling conflicts could not be worked out.
Six original feature films will be anchored by three upcoming sequels over the course of the next four years.
The 30 Rock actor to play Dennis in the musical, starring Tom Cruise, Mary J. Blige and Julianne Hough.
Jude Law, Alec Baldwin and Isla Fisher also join DreamWorks Animation's 3D epic.
Tom Cruise and Gwyneth Paltrow still in talks for Adam Shankman's musical.
Sharlto Copley also joins the Will Smith-starring Columbia Pictures tentpole.
Tina Fey, Alec Baldwin, and Tracey Morgan go behind the scenes of this Thursday's live episode of 30 Rock.