The Reds optioned Dunn to Triple-A Louisville on Monday.
Dunn entered spring training as one of eight outfielders on the 40-man roster and was one of the lesser-established options at the big-league level, so he needed a big showing in the Cactus League to have a realistic shot at making the Opening Day squad. The 27-year-old was unable to deliver, hitting just .136 with five strikeouts in 22 at-bats this spring before the Reds demoted him. He should get the chance to play regularly at Louisville to begin the season.