Imagine TV president David Nevins is expected to be named to replace Robert Greenblatt at Showtime.
Nevins was selected to take over as entertainment president at the pay cable network by Matt Blank after Greenblatt told CEO Blank he wanted to leave.
A Showtime spokesman had no comment.
Greenblatt has been with Showtime for seven years and has been on a hot streak with original series including Dexter, Weeds, United States of Tara, Californication, The Tudors and Nurse Jackie.
News of Nevins' departure from Imagine was first reported by Deadline.com, and his ties to the Showtime job was first reported by Variety.com.