Athletic director Barry Collier said in a statement Thursday that assistant Chris Holtmann will serve as interim coach until Miller returns.
Holtmann won a school record 21 games and was chosen Big South coach of the year in his final season as Gardner Webb's head coach in 2012-13.
The Bulldogs open practice Saturday.
Miller played college basketball at Butler and also served as an assistant coach with the Bulldogs before he was hired as Brad Stevens' replacement in July 2013. The 35-year-old Miller led Butler to a 14-17 record in his first season as coach, the Bulldogs' first season in the Big East.