Wacha -- the Cardinals' fourth-ranked prospect, according to MLB.com -- was scratched from a scheduled Monday start for Triple-A Memphis.
The 6-6, 210-pound Texarkana, Texas native is currently 4-0 with a Pacific Coast League-leading 2.05 ERA in nine starts for the Memphis Redbirds. Wacha has allowed just 35 hits in his 52.0 innings pitched this season for a .187 opponent's batting average.
Robert Falkoff is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.