The Iron Man superhero star is putting off writing his book for which HarperCollins publishing company has already paid him, according to a report from the Associated Press.
The reasons are still unknown why Robert Downey Jr. has put the literary project aside. The book was supposed to give fans a "candid look at the highs and lows of his life and career."
The 43-year-old actor, who has mellowed out over time, experienced personal setbacks in the past, such as problems with drugs and the law.
Moviegoers can next see him play alongside Ben Stiller and Jack Black in the comedy Tropic Thunder.