In the 2016–17 season, O'Leary appeared as a substitute in Connacht's opening five Pro12 games, and in the opening two rounds of the Champions Cup. He didn't in the Pro12 clash with Leinster, but returned for the following round against Newport Gwent Dragons. That month however, O'Leary suffered a concussion injury in training. This injury ruled O'Leary out for some time and he failed to make an appearance for the first team for the remainder of the season. In April 2017, it was announced that O'Leary would depart Connacht at the end of the season.