Cincinnati is designating Petty as its 27th man for the twin bill, so he's expected to be returned to Louisville once the doubleheader concludes. The 22-year-old righty will be making his MLB debut Wednesday after turning in a 3.52 ERA, 1.30 WHIP and 27:9 K:BB across 23 innings over his first five starts of the season at the Triple-A level.