But Williams and Davies, who both featured in the Six Nations, will take their Scarlets partnership on to the international stage in his stead.
The backline will feature two more Scarlets, in George North and Rhys Priestland, while hooker Ken Owens comes in for his club teammate Matthew Rees.
Australia come into the game on the back of a shock defeat to Scotland on Tuesday and will be missing several front line players through injury.
But despite those absences caretaker coach Rob Howley is expecting a stern test from the Wallabies.
He said: "Australia will be disappointed after their defeat to Scotland, but that will make them all the more dangerous for us.
"The Wallabies are still the second highest placed side in the world rankings and we are playing them in their own back yard.
"We all appreciate the enormity of the task ahead of us, the long-term stats don't make happy reading for the Welsh against the Wallabies.
"As recently as this season we have two losses racked up against Australian opposition and we are determined to stop that trend."
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