Brewster quit her role as Emily Prentiss in February and will be replaced by new regular Jeanne Tripplehorn, playing FBI agent Alex Blake.
"It would be fantastic [if Paget came back], but it's too early to make those decisions," Messer told TV Guide. "It takes a lot of people to sign off on things like that."
However, the producer promised that the Prentiss character will be referenced frequently in the show's eighth season.
"In the premiere, we learn that Morgan (Shemar Moore) and Garcia (Kirsten Vangsness) visited with Prentiss while they were in London," she explained. "We'll mention her as often as possible. She's gonna be loved."
Criminal Minds star Joe Mantegna (David Rossi) previously hinted that Brewster could return to the show as a guest star, hinting that her character "is positioned in a way that she can come back periodically".
The actress will next be seen in the 14th-season premiere of NBC crime drama Law & Order: SVU.
Criminal Minds returns to CBS on Wednesday, September 26 at 9/8c. The series airs on Sky Living in the UK.
> Criminal Minds casts Josh Stamberg for season eight
> Matthew Gray Gubler signs two-year deal with Criminal Minds
Watch Digital Spy's recent interview with Criminal Minds star Kirsten Vangsness below: