Cardinals manager Oliver Marmol said that O'Brien (forearm) will throw a live batting practice session at Double-A Springfield on Wednesday, John Denton of MLB.com reports.
O'Brien will throw approximately 20-to-25 pitches Wednesday, and if all goes well, he could be cleared to begin a rehab assignment with Springfield this weekend. The 29-year-old righty has been on the injured list since late March with a right forearm strain. He's expected to fill a low-leverage role out of the St. Louis bullpen once he's activated from the 60-day injured list.