O'Brien (forearm) was transferred from the 15-day injured list to the 60-day IL on Friday, John Denton of MLB.com reports.
O'Brien's transfer to the 60-day IL makes room on the 40-man roster for Kolton Ingram, who was acquired off waivers. O'Brien was close to starting his throwing program in mid-April, but no updates have been provided since. He'll be eligible for reinstatement May 30, though it seems far from definite that he'll be ready for immediate action.