The Diamondbacks outrighted Miller to Triple-A Reno on Friday.
Miller cleared waivers after Arizona designated him for assignment last week when it needed to clear a 40-man roster spot for the newly signed Wilmer Flores. The southpaw reliever will likely open the upcoming campaign at Reno, where he posted a 7.71 ERA and 52:63 K:BB across 42 frames in 2018.