Several characters will compete for the role in the NBC comedy's new season, with the frontrunners thought to be Jim, Andy (Ed Helms) and Dwight (Rainn Wilson).
However, Krasinski told Screen Junkies: "I don't think Jim was made for the leadership role. I think he's a really good middleman and he's a good cushion and filter for the rest of the office [but] I don't see him running the office any time soon."
The actor added that Jim will begin enjoying his work more in the sitcom's upcoming eighth run.
"Pam (Jenna Fischer)'s pregnant and Jim's finding it a lot more fun to be at work and just providing for his family," he explained. "He starts to feel like, with the office being run a little more efficiently, he can have a lot more fun himself."
Krasinski also suggested that the new episodes of The Office are reminiscent of the show's earlier years.
"It feels a lot like the first couple seasons where... inter-office relationships are the thing that was so fun," he said. "I know that I have a lot of fun stuff with Andy who needs my help in different ways, shapes and forms, [and] I have a lot of stuff with Kevin (Brian Baumgartner), which is great."
The eighth season of The Office begins on Thursday, September 22 on NBC.
> Ed Helms: 'The Office has no leading man'
Watch a clip of John Krasinski on The Office below: