Australian head coach Andrew McDonald has revealed that Australia's XI for the final Test against South Africa at the Sydney Cricket Ground could see radical changes.

Australia will be forced to make at least two changes, with both Mitchell Starc and Cameron Green missing out, and now set to race the clock to be fit for the four-Test Border-Gavaskar Trophy in India during February and March.

The duo both suffered finger injuries during the most recent Test at the Melbourne Cricket Ground, where Australia wrapped up the series against the Proteas and all but locked up their spot in the World Test Championship final, which will be played at The Oval in London during June, just before the Ashes tour of England gets underway.

Australia's 14-man squad for the final Test of the summer saw Ashton Agar, Lance Morris, Marcus Harris and Matt Renshaw all called up, while Josh Hazlewood is also set to make his return.

It means Agar and Renshaw are in what would appear to be a direct battle for Green's spot, with any chance of Agar being selected likely hinging on wicket-keeper Alex Carey moving up to number six in the batting order.

Speaking to the media, McDonald didn't rule out the idea of playing five specialist bowlers.

"There are so many options depending on what the surface offers in terms of the balance of the attack," McDonald said.

"It could be two spinners, two quicks. We could play a slightly more aggressive team with Alex Carey going to six, and play five bowlers.

"Or we could play probably what we'd call a normal structure for Australia where it's three quicks and one spinner and some part-time spin options to help out."

Agar's selection in the squad to play the Proteas this week appears to indicate he has the inside running on a spot in the touring party to India next month, although is no guarantee, with incumbent Mitch Swepson, and young gun Todd Murphy, as well as Australian white ball leg spinner Adam Zampa all pushing to be the second option to Nathan Lyon.

Starc's replacement is also up in the air, with Lance Morris gunning for a Test debut.

Australia's fastest bowler would be more of a like-for-like replacement than the returning Hazlewood, although it's unclear how many fast bowlers will ultimately be selected.

Scott Boland is no guarantee to keep his spot, with captain Pat Cummins the only quick locked into the attack.

McDonald admitted that if Australia need extra pace then Morris is likely to play.

"All scenarios are on the table," McDonald said.

"If we feel as though we need some air-speed then Lance is the obvious one. The conditions will determine that."

The third and final Test of the series at the Sydney Cricket Ground starts at 10:30am (AEDT) on Wednesday, January 4.