Mikolas won't throw his scheduled bullpen Wednesday, as his shoulder soreness isn't progressing as the Cardinals hoped, Justin Toscano of The Bergen Record reports.

A forearm injury cost Mikolas all of last season, but it's a shoulder problem that's bothering him so far this year. The issue has so far been characterized as mere stiffness or soreness, but this latest setback indicates that there could be something worse going on. The Cardinals should find that out after Mikolas undergoes further tests. This delay is already casting his readiness for Opening Day in some doubt, and it's possible he winds up being forced to miss an extended period.