Adding to this week’s trend of superhero bailouts in the form of Stuart Townsend leaving Thor and the entire cast and crew of Spider-Man 4 bailing out with Sony rebooting the franchise, another superhero has dropped out of a project. Well, not exactly, but Robert Downey Jr. and has removed himself from director Jon Favreau’s Cowboys & Aliens.

According to a source of the LA Times, Downey has left and DreamWorks is now searching for their new lead to ride into the sunset full of UFOs. Favreau will still be directing and the plan is to begin principal photography this year for a summer 2011 release.

With RDJ out, a replacement is needed for the role of Zeke Jackson, the hero who leads the gunslingers of the wild west against the pesky extra-terrestrials.  DreamWorks will have to find a popular star to fill those shoes.

We’re not sure yet on the exact reason for Downey’s dropping out but it’s reasonable to assume he may just have too much on his plate going forward. With this holiday’s Sherlock Holmes kicking off another great franchise, there could be a rush from the studio for a sequel which they spent a lot of time and effort setting up for in this first installment. [Update: We have confirmation that the Sherlock Holmes sequel is the reason that Downey Jr. dropped out of this film.]

That’s not all for the comeback star however, as he also has at least another two leading roles in Marvel Studios’ franchise as Tony Stark/Iron Man after Iron Man 2 debuts this May. Downey simply may not have time to dedicate two a third potential franchise.

The sci-fi western will surely be a hit with such major players involved as Alex Kurtzman, Bob Orci and Damon Lindelof penning the script, producing alongside Steven Spielberg. And of course, Jon Favreau will be helming the project as director.

Who do you think can take over the lead role in Cowboys & Aliens?

Iron Man 2 kicks off this summer on May 7, 2010. Cowboys & Aliens may start shooting in July.

Source: LA Times (via IESB)