Downey Jr., who played the lead role of tycoon-turned-superhero Tony Stark in the 2008 comic book movie, will reprise his role.
He insists reports that 'The Wrestler' star has already signed up to play comic book villain Crimson Dynamo are 'false'.
"That's actually incorrect," the Daily Express quoted him as telling MTV.
However, he refused to confirm Rourke is in negotiations to play another character, Whiplash.
"I can neither confirm nor deny that. Or maybe it's some semblance of both. I can tell you everything about the story except I won't give away the ending. The nerd stuff is top-drawer security," he added. (ANI)