Puk was shut down with biceps soreness Wednesday, Susan Slusser of the San Francisco Chronicle reports.
Puk had an MRI, which revealed no structural damage. He's expected to resume throwing soon. Arm issues are never a good sign for a young pitcher, though there's no evidence yet that this particular one will be a threat to Puk's season. He was reassigned to Oakland's minor-league camp Sunday but is expected to join the big-league rotation at some point this summer. That timeline would be altered if Puk's injury turns out to be more serious than initially believed.