Faletau replaces Scarlets back row Rob McCusker, who withdrew last week to treat a hernia.
Also training with the national squad this week, but yet to receive full call-ups are Blues centre Dafydd Hewitt, Scarlets centre Scott Williams and London Wasps back row Andy Powell.
Powell is unavailable for the visit of the Wallabies this weekend.
Injured centre Jonathan Davies, who sustained ankle ligament damage in training last week, has now withdrawn from the squad.
Toby Faletau stats
International record - uncapped
Date Of Birth: 12/11/1990 (19)
Height: 188cm / 6'2"
Weight: 108kg / 238lbs / 17st