The Braves released O'Brien on Monday.
O'Brien (undisclosed) was placed on the 10-day injured list Thursday, Andersen Pickard of MLBDailyDish.com reports.
O'Brien will be a part of the Braves' 60-man roster, Gabe Burns of The Atlanta Journal-Constitution reports.
O'Brien joined the Braves as a non-roster invitee Wednesday.
O'Brien (ribs) went 0-for-3 with a walk and a strikeout in his first game back with Triple-A New Orleans on Tuesday.
O'Brien (ribs) cleared waivers and was outrighted to Triple-A New Orleans on Saturday, Jordan McPherson of the Miami Herald reports.
O'Brien (ribs) was designated for assignment Thursday, Jordan McPherson of the Miami Herald reports.
O'Brien (ribs) will begin a rehab assignment with High-A Jupiter on Tuesday, Jordan McPherson of the Miami Herald reports.
O'Brien was placed on the 10-day injured list with a left rib cage contusion Saturday.
O'Brien is out of the lineup for Sunday's game against the Braves, Joe Frisaro of MLB.com reports.