UPDATE TUESDAY 11AM: A source close to CBS stressed that the casting changes on Criminal Minds were a creative, not financial decision, and a way to “refresh a veteran drama series.” A new regular female cast member will be brought in sometime next season to fill the void that will be left by Cook’s departure.

EXCLUSIVE MONDAY 7:50PM: Heading to Season 6, CBS’ successful crime drama Criminal Minds is trimming the female portion of its cast for what I hear are financial reasons. I’m told the option of series regular A.J. Cook has not been picked up and co-star Paget Brewster is being made an offer to stay for only a reduced number of episodes next season, leaving fan favorite Kristen Vangsness as the only remaining full-time female cast member. I hear negotiations are underway with Brewster for a new deal that would keep her on the show. If she agrees, she will continue to be formally a regular but won’t appear in every episode. Talks are also ongoing with Cook to possibly appear in several episodes next season to wrap her character Jennifer Jereau’s storyline.

Among the broadcast networks, CBS has been aggressive in trying to rein in series costs, especially on its longer-running, more expensive dramas with large ensemble casts. Criminal Minds has had seven regulars as part of its core cast. Staying on are Joe Mantegna, Thomas Gibson, Shemar Moore, Matthew Gray Gubler and Vangsness. With the exception of Vangsness’ quirky nerd goddess Penelope Garcia, which has developed a strong following, the series has largely been perceived as a male-centered ensemble, with the boys getting most of the action.

Cook has been on the show since the first episode, joining after the pilot in 2005. Paget Brewster came on board nine episodes into Season 2, replacing original cast member Lola Glaudini. But aside from the Glaudini-Brewster switch and the forced replacement of original lead Mandy Patinkin with Mantegna following Patinkin’s abrupt exit after Season 2, the cast on Criminal Minds has been pretty stable, with Gibson, Moore and Vangness all on board since the pilot.