Siddle spent the winter recovering from a back injury sustained last February with the 31-year-old replacing Jon Holland.

Australia vice-captain David Warner backed Siddle to be at his damaging best against South Africa.

"Credit to him (Siddle) for getting himself ready and fit," Warner said.

"He's bowing faster than I've faced in previous times.

"He feels fit, he's bowling good line and length, and he was troubling our batsmen in the nets.

"He's one of those bowlers when he hits (a difficult) line and length and there's a little bit in that wicket he's hard to face.

"He's been our rock for many years now and he's got the games under him and the experience to know what to bring out here."

South Africa are expected to name their starting XI tomorrow morning.

Australia XI: Steve Smith (c), David Warner, Shaun Marsh, Usman Khawaja, Adam Voges, Mitchell Marsh, Peter Nevill, Mitchell Starc, Peter Siddle, Nathan Lyon, Josh Hazlewood, Joe Mennie (12th man).