Despite inking a deal to return to the police procedural drama earlier in the year, it has now emerged that Petersen's role in the ninth season will be greatly reduced.
Carol Mendelsohn, executive producer of the CBS show, disclosed that Petersen will remain involved in a production capacity and make occasional guest appearances.
"He will, whenever CBS asks, come back. I don't think you've seen the last of Gil Grissom," she said.
Petersen said of his new CSI role: "I'm in a great place in terms of knowing that I'll be more free to make choices. And I'm responsible enough to not do it in a way that would hurt [the show].
"I want it to work for the writers, I want it to work for the cast, and, most importantly, I want it to work for the audience. I don't want them to abandon the show."
With Petersen's departure, along with those of Jorja Fox and Gary Dourdan, Mendelsohn admitted that the ninth season would be "a year of transition for the show".