O'Brien (forearm) will begin a throwing program this week, Katie Woo of The Athletic reports.
An MRI on O'Brien's right forearm showed no structural damage, but the team decided to shut him down for a few weeks regardless. It sounds like O'Brien is about ready to begin ramping up his throwing, and provided he avoids any setbacks, a return in mid-to-late May seems plausible. O'Brien has made single appearances in the majors each of the past three seasons, all for different teams (Reds, Mariners, Cardinals).