"Franco will be appearing in 'Alien: Covenant' as Branson, the captain of the Covenant and husband of Katherine Waterson's [character] Daniels," according to AvPGalaxy, a fan site dedicated to "Alien," "Predator" and "Alien vs Predator" that published the rumor as an exclusive.
20th Century Fox did not immediately respond to a request for comment.
In director Ridley Scott's "Alien: Covenant," the crew of colony ship Covenant discover what they think is an uncharted paradise.
But it's actually a dangerous world whose only inhabitant is the synthetic David, played by Michael Fassbender. He's a survivor of the doomed Prometheus expedition.
AvPGalaxy also says Franco's role as Branson is small, with his character showing up in the film's first 10 minutes.
Maybe Franco's only briefly in the film due to his busy acting schedule that includes him starring in 14 other movies and a TV series next year.
The film also stars Noomi Rapace reprising her role as Dr. Elizabeth, as well as actors Katherine Waterston, Danny McBride, Billy Crudup and Guy Pearce.
"Alien: Covenant" is scheduled to debut in theaters on May 19, 2017.