Wacha was diagnosed with a right shoulder strain and won't be throwing for at least a few more days, Anne Rogers of MLB.com reports.
Wacha had the diagnosis confirmed by an MRI on Thursday and while he appears to have avoided a serious injury, he's unlikely to be available for the National League Division Series should the Cardinals qualify. The 28-year-old was pitching well prior to the injury with a 2.89 ERA and 1.37 WHIP in his last nine outings.