Cardinals manager Oliver Marmol said Friday that O'Brien will be shut down for a few days due to a mild right calf strain, Brian Murphy of MLB.com reports.
It will take a couple weeks for O'Brien to ramp things back up, so it will be at least the beginning of March before he's ready to pitch in spring training games. O'Brien is also now unlikely to pitch for Team South Korea in the World Baseball Classic, though he will remain in the player pool in case there's a chance he can be added later. The injury could also affect O'Brien's chances at opening the season as the Cardinals' closer. He is in the mix for saves with JoJo Romero and perhaps Matt Svanson.