It was /gravity-wants-sandra-bullock/reported earlier this month that Sandra Bullock was in talks for the lead role. Deadline now indicates that Bullock is "locked in" for this role. The screenplay heavily revolves around Bullock's character, an astronaut who is trapped in deep space when an asteroid field takes out her space station. Robert Downey Jr. would have played a smaller supporting role, as the only other surviving astronaut.
Warner Bros. has denied that Robert Downey Jr. is leaving the project, saying that the scheduling issues are expected to be resolved. Downey was originally set to shoot Gravity before Sherlock Holmes 2 began filming. Then it was reported that he would take a break in the middle of shooting Sherlock Holmes 2 to film his role in Gravity. Now neither scenario seems plausible, with Sherlock Holmes 2 already well into production.