A Entertainment Weekly report that discussed Robert Zemeckis being the front-runner to direct The Flash, also suggested that Billy Crudup had left project after it went into production delay.
We decided not to report this due to the fact that when an actor signs up for a DC Extended Universe film, they sign a multi-film deal, meaning the idea that he can leave without some major legal hurdles was ridiculous to begin with. As we’ll see Bill Crudup as Dr. Henry Allen in Zack Snyder’s Justice League.
The Entertainment Weekly scoop also mentioned that both Sam Raimi and Marc Webb passed on the job of directing The Flash, but with this being revealed as false, its likely the same for that scoop.
Source: The Hollywood Reporter