Paul Lieberstein is believed to be keen to focus on a planned Office spinoff featuring Rainn Wilson's character Dwight Schrute, according to Entertainment Weekly's Inside TV blog.
NBC is thought to be actively seeking a replacement for Lieberstein, who is a producer and chief writer on the show. However, it is thought that he will continue to play HR manager Toby Flenderson on the programme.
Lieberstein took over The Office in its fifth season and the new show is currently at the development stage.
Wilson revealed at this year's Screen Actors Guild Awards that NBC is currently "mulling over" the proposed spinoff, saying: "It would be even more far-out than The Office... it's a good idea."
James Spader, who joined the show as Robert California full-time at the start of the eighth season, recently announced that he will be leaving the programme.
Negotiations are also thought to be continuing with the current cast for a ninth season.