Pitt was originally to star in the big-screen thriller as a journalist but the actor quit during pre-production, citing concerns with the script, contactmusic.com reports.
Gladiator star Russell Crowe was roped in as a late replacement for Brad to star opposite actor Ben Affleck's character of a Congressman in the film.
Director Kevin McDonald is convinced that Crowe's rough features are more suited to the role.
"In a way, I was lucky it didn't work out with Brad. The relationship between the journalist and the politician was meant to be between somebody who feels inferior, who's a bit of a schlump, who kind of can't get a girlfriend, and somebody he's looking up to and admires his polished politician friend," he said.
"That is not the dynamic of a Brad Pitt. He's not looking up to anyone thinking 'Oh, I wish I could have your girlfriend'," he added.