Leiter was optioned to Triple-A Iowa on Saturday, Meghan Montemurro of the Chicago Tribune reports.
Leiter has failed to impress in three starts and one relief appearance this season. He owns a 7.84 ERA and 1.74 WHIP, striking out just 20.4 percent of opposing batters while walking 14.3 percent. Locke St. John was recalled to take his place on the roster.