The 'Sherlock Holmes' actor - who stars as the superhero in the eponymous franchise as well as the 'Avengers' movie series - admitted there is nothing in the pipeline for Tony Stark's solo adventures following the release of Iron Man 3 last year.
He told Variety.com at the Toronto Film Festival: "There isn't one in the pipe. No, there's no plan for a fourth Iron Man."
However, the 49-year-old actor will reprise the character in the upcoming Marvel blockbuster Avengers: Age of Ultron, which is set for release on April 24 2015, and has already signed up for the third comic book superhero team-up.
Robert also revealed that his future as the character is out of his hands.
When asked if he would mind another actor taking over the role, he joked: "I like that the idea is that it would be up to me, like I'm casting director for Marvel."
Meanwhile, Robert's latest offering 'The Judge' - in which he co-stars with Robert Duvall and 'Gossip Girl' actress Leighton Meester - recently premiered in Toronto and is set for UK release on October 17.