The 47-year-old actor, who plays billionaire crime fighter Tony Stark in the series, suffered an ankle injury in August during a stunt sequence, forcing the movie to shut down so he could recover, reported E! online.
After a month of recuperating, Downey Jr returned to work in Miami earlier this week to finish shooting the remaining scenes.
The film is set to hit theatres in May 2013 and also stars Gwyneth Paltrow, Don Cheadle and Guy Pearce in pivotal roles.