Affleck had been set to star as Don Haskins, who coached an all-black starting lineup at Texas Western -- now the University of Texas at El Paso -- to an NCAA men's basketball championship in 1966. It was the first all-black lineup to win the title.
According to Variety, Disney said Affleck withdrew from the project due to scheduling conflicts. However, the paper said there were reports in Hollywood that Affleck could not come to terms on a deal with producer Jerry Bruckheimer.
Lucas is best known as the star of such features as "Hulk" and "A Beautiful Mind."