ARU chief financial officer Todd Day has announced his resignation.
Day is the third executive to move on from their post in as many months, with ARU chief operating officer Rob Clarke another high-profile departure last month.
The national body's finance head is believed to be joining the Australian Olympic Commission, after close to seven years as the ARU CFO.
Before joining the ARU, Day was the Waratahs CFO for five years.
Day's successor has already been nominated, with Sharon Hrycek promoted to the CFO position with Day's departure.
The change comes amid a tumultuous year for Australian rugby, on and off the field, with the makeup of Australian Super Rugby teams still uncertain.
RugbyWA and the ARU are set to begin arbitration next week, while Rebels owner Andrew Cox has reportedly looking at selling the franchise's licence back to the Victorian Rugby Union, though that would need ARU approval.