Miller was optioned to Triple-A Nashville on Sunday, Curt Hogg of the Milwaukee Journal Sentinel reports.
Miller was called up from Nashville in late April and appeared in three games during his time with the Brewers, allowing one run on three hits with two strikeouts and no walks across 4.2 innings. He has a 1.42 ERA over 12.2 frames at Triple-A this year and should rejoin the big club at some point later in the season.