The Guardians traded Rivera to the Reds on Monday in exchange for Nathaniel Lowe, Zack Meisel of The Athletic reports.
Rivera, 19, got lit up in his lone start at Single-A, but he dominated the Arizona Complex League to the tune of a 2.44 ERA, 1.04 WHIP and 70 strikeouts in 48 innings. The Venezuelan righty is undersized at 5-foot-10 but won't turn 20 until the offseason.