Momoa, 41, shared a photo of Fisher, 33, at a San Diego Comic-Con event with the words, “#IStandWithRayFisher” on the photo.
The two actors appear in Justice League with Momoa playing Aquaman and Fisher as Cyborg.
In July, Fisher claimed on Twitter director Joss Whedon “was gross, abusive, unprofessional, and completely unacceptable,” while working on the 2017 action film, adding that Whedon “was enabled, in many ways, by Geoff Johns and Jon Berg.”
Johns is an American comic book writer who served as the President and Chief Creative Officer of DC Entertainment from 2016 to 2018, while Justice League was being made. Berg was a producer for the film.
In August, Fisher had added more details to his complaint, writing that Johns “summoned me to his office to belittle and admonish my (and my agent’s) attempts to take grievances up the proper chain of command” and “made a thinly veiled threat to my career.”