Wacha winced after throwing ball four to Philadelphia's Rhys Hoskins with two outs in the fourth inning.
Pitching coach Mike Maddux initially visited the mound before waving for the team trainer to come out. Wacha was removed from the game and the Cardinals announced the nature of the injury a short time later.
He will undergo an MRI exam Thursday in Milwaukee, and multiple media outlets reported that he is headed to the disabled list.
He served up a two-run homer to Cesar Hernandez earlier in the inning.
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