Australia have confirmed replacements for Mitchell Starc and Cameron Green in their 14-man squad for the third Test against South Africa.

The Test, to be played at the Sydney Cricket Ground from January 4, will be Australia's final red-ball hit out of the summer, and final Test before embarking on a four-Test tour of India for the Border-Gavaskar Trophy in February and March.

Starc and Green will both miss out after suffering finger injuries during the Boxing Day Test at the Melbourne Cricket Ground, with the duo now racing the clock to be fit for India.

While the duo hit the recovery room, Australia will be boosted by the return of new-ball bowler Josh Hazlewood for the Sydney Test.

Lance Morris also retains his place in the squad, while three new additions have also been called up in Marcus Harris, Matthew Renshaw and all-rounder Ashton Agar.

Harris has been part of the squad throughout the summer as a back up top-order option, while Renshaw's form at Sheffield Shield level has been excellent since his move to the middle order.

"Matthew is included as a versatile batting option who is in good form, including an unbeaten century in the recent PM's XI tour match against the West Indies," said selector Tony Dodemaide in a statement.

It would appear that Renshaw is in a direct battle with Ashton Agar for a spot in the top seven, pending on whether Australia wants to play a second spinner and an all-round option in Sydney.

If Agar plays, expect him to bat at number seven, with Alex Carey moving to number six, otherwise, Renshaw would bat at either five or six, with Travis Head filling the other spot in a flexible batting order.

In the bowling attack, Pat Cummins and Nathan Lyon are certain to play, with Scott Boland, Lance Morris and Josh Hazlewood fighting for the other two spots.

The selectors have hinted that Morris, who has raw pace, is a chance of making his debut in what would be a direct swap for Starc and a move that will give the bowling attack extra firepower that it won't have with three similar right-arm bowlers in Hazlewood, Cummins and Boland, although it would be difficult to leave any of the trio out.

"It's a blessing to have Josh (Hazlewood) returning while Lance (Morris) offers a genuine point of difference with his raw pace and skill," Dodemaide added.

"This squad will cover all bases for when we get to Sydney and assess the conditions closer to the Test match."

Intriguingly, Todd Murphy and Mitch Swepson, who were both thought a chance of being included for Sydney, have been left out of the 14-man squad.

The Test, which is a dead rubber, but still has World Test Championship points up for grabs, will get underway on January 4.

Australia squad for third Test vs South Africa

Pat Cummins (c), Ashton Agar, Scott Boland, Alex Carey, Marcus Harris, Josh Hazlewood, Travis Head, Usman Khawaja, Marnus Labuschagne, Nathan Lyon, Lance Morris, Matthew Renshaw, Steve Smith (vc), David Warner