O'Brien is managing calf soreness that is being evaluated Tuesday, Jeff Jones of the Belleville News-Democrat reports.
It's unclear exactly how O'Brien sustained the injury, but it puts his availability in question for Team South Korea for the upcoming World Baseball Classic. After recording six saves and six holds with a 2.06 ERA, 1.15 WHIP and 45:22 K:BB over 48 innings last year, the 31-year-old righty is expected to be in the mix for saves to begin the year for St. Louis.