Carell made his final appearance on the NBC comedy last week in what he described as a "bittersweet" exit.
While it was previously suggested that his successor had already been chosen from a host of guest stars due to appear in the season finale, Krasinski denied having any knowledge of who might join the cast full time.
"You know what's so funny? We're trying to figure it out off camera, so we figured why not do it on camera too?" he explained to Access Hollywood.
"So all these people are coming in and doing us a solid and helping us out, but at the same time, we haven't figured out who's going to do it, which is kind of fun. It's kind of very real, very honest."
The Office two-part season finale, due to air later this month, will include appearances by Catherine Tate, Ray Romano and James Spader as well as Will Arnett.