Wallabies forwards coach Dan McKellar quit on Wednesday just months before the Rugby World Cup and will reportedly take the top job at English Premiership side Leicester.
McKellar first joined the national set-up in 2021 while head coach of the Brumbies and was widely touted as the heir apparent to former Australia boss Dave Rennie.
But when Rennie was sacked in January, ex-England coach Eddie Jones was appointed instead.
Rugby Australia said McKellar had resigned with immediate effect "to take up a coaching position overseas". Australian and British media said he was headed to Leicester.
"This was an extremely difficult decision to make but it's one that's made with my best professional and family interests in mind," said McKellar.
"I firmly believe my next challenge will make me a better coach and hopefully allow me to return home and contribute in a positive fashion to Australian rugby in the future."
National scrum coach Petrus du Plessis also quit to pursue interests outside of the sport.
Rugby Australia said it was working on finalising the coaching staff to join Jones in the lead-up to the World Cup in France in September-October, with announcements in due course.
"We are disappointed that Dan will not continue with the Wallabies this year," said Rugby Australia chief Andy Marinos.
"Together with Eddie we will continue to work hard to assemble a quality coaching staff to deliver a high-performing environment in our preparation for the Rugby Championship and Rugby World Cup later this year."