"He's not going to do it," Ken Sunshine, a spokesman for Affleck, said Wednesday. "We're not going to get into any details. ... It will be a good project for somebody."
Haskin's 1966 team was the first ever to win a national title with five black starters.
"We're looking for other actors," said Claire Cooper, the movie's unit publicist. "We still plan to start production in August."
Haskins, who coached 38 years at the school now known as the University of Texas at El Paso, said last week he'd heard Affleck had yet to sign his deal.
"I'm disappointed, but I know they'll find the right person," Haskins said.
Haskins has always been a reluctant hero about his role in changing sports history, saying he simply picked the best players for the 72-65 win over Kentucky's heavily favored and all-white basketball powerhouse.
After the victory, universities all over the country increased their recruiting of black players.
Trade journals reported Wednesday that Disney is considering Josh Lucas (search), who has appeared in Ang Lee's "Hulk," "Sweet Home Alabama" and "A Beautiful Mind. Cooper said she couldn't confirm that Lucas is under consideration.