Davis was recruited in May from English Premiership side London Irish, and has returned to Britain for family reasons.
They have a quality replacement in Ryles, who worked with Jones when he was England boss and is considered one of the hottest young coaches in rugby league.
“Jason is the most sought-after coach in the NRL,” said Jones, who needs all the help he can get with Australia losing four consecutive Tests since he took over.
“He will add immensely to our coaching staff and help prepare the players to win the Rugby World Cup. We are thrilled to have him join the team.”
Ryles played 271 games in the National Rugby League before turning to coaching with Melbourne Storm and Sydney Roosters.
“It has come out of the blue, obviously, and it’s all been very quick,” he told the Sydney Morning Herald.
“I will be assisting Eddie and the guys with attack. Obviously they have all their systems in place and I won’t be coming in reinventing any wheels.
“It is just assisting where I can and being as useful as I possibly can while I am over there, helping out.”
Australia’s inexperienced squad left for France on Thursday with Ryles jetting over imminently.
The Wallabies open their World Cup campaign against Georgia in Paris on September 9 before facing Fiji, Wales and Portugal in Pool C.
