It was previously reported that Joaquin Phoenix was in the running for the role of Clyde Tolson, but Eastwood has now brushed off the claims.
"I don't know where that came from... didn't he become a rapper?" the director told Reuters.
"It's a great role for him," Eastwood said of DiCaprio taking on the role of Clyde.
He continued by saying that DiCaprio is in the process of agreeing a contract for the film but that it is yet to be signed.
The film will follow Hoover's life upon becoming the first director of the FBI through to the controversy surrounding his sexuality in the years following his death.