O'Brien was reassigned to minor-league camp Sunday.
O'Brien spent the majority of the 2021 season at Triple-A Louisville and worked primarily as a starter. He racked up a 4.55 ERA and 1.32 WHIP across 112.2 innings in the minors and was rewarded with a spot start in Cincinnati to close the campaign. O'Brien could return to the majors as the season progresses if the Reds suffer injuries to their rotation.