Foster was removed from an appearance at Triple-A Norfolk on Thursday due to right shoulder discomfort, Roch Kubatko of MASNSports.com reports.
Foster was charged with one run over 1.1 innings of work before being pulled. It's unclear whether Foster will be sent for an MRI, but even if his removal was precautionary, he'll likely be unavailable for at least a few days. The 27-year-old has allowed 10 runs (nine earned) with a 9:8 K:BB over nine innings covering six relief outings during his time with the Orioles this season.