The "Avengers" star confirmed the news to Variety at Disney's D23 Expo on Saturday.
Ruffalo joined Marvel's Kevin Feige onstage to share an exclusive trailer of "Avengers: Infinity War" alongside other Marvel Cinematic Universe favorites.
Following the screening Ruffalo spoke about a potential spin-off of his own.
"I want to just make one thing perfectly clear today: A standalone 'Hulk' movie will never happen. Universal has the rights, and for some reason, they don't know how to play well with Marvel. And, they don't want to make money," Ruffalo said.