Ron Howard refused to direct The Phantom Menace because it was “too daunting”
Reminder: the newly appointed Han Solo movie director Ron Howard had revealed that George Lucas asked Steven Spielberg, Robert Zemeckis and Howard himself to direct The Phantom Menace.
Source : Happy Sad Confused Podcast (11/22/2015)
UPDATE : Howard had later clarified that there wasn’t a script yet.
Source: Metro
(This video was dug out by MakingStarWars)