"I haven't seen any 'signed' paperwork, but there's a lot of talk," Zimmer, who plays studio exec Dana Gordon, told Us at Sunday's Elizabeth Glaser Pediatric AIDS Foundation Carnival in L.A. "I think that it's more than a possibility. I actually think that it's going to happen."
Though there's no finale episode written yet for Kevin Dillon, Adrian Grenier, Kevin Connolly and Jerry Ferrara, Zimmer, 39, says the last eight episodes serve as a strong lead-in to a film.
"[The storyline] definitely ends in a way where you're going to want to see all of the characters, and wonder, 'Oh my God, now what happens?!'" says Zimmer, who appears in four of the episodes. "Now that we've gotten to this place in their lives, you're definitely going to want to see more."
As plans for a film continue to evolve, Zimmer tells Us the cast is having an easier time accepting the end of the TV series in its current form.
"It's bittersweet, but I think that there's such a sense of hope knowing that we're probably going to do a movie," she says. "When the movie is done, that's when it's going to be sad. All the guys are friends in real life, and they're all going to hang out, but I'll just be sad to see the characters go away once the movie is done."
Entourage premieres July 24 at 9 p.m. (EST) on HBO.