Marsh missed Australia's heavy loss in the Perth series opener because of an abscess on his buttock.

"He is pretty positive that he'll be right for Friday," Australia's vice-captain Alex Carey told reporters on Wednesday.

"Shaun obviously last series over in England was sensational, he scored two hundreds for us.

"So for SOS (Marsh) to come in at three and probably play a bit of an anchor role around some of those top order explosive players ... it's a little bit of stability up the top, hopefully."

Australia sank to a six-wicket loss in Perth with the South Africans coasting to victory with 124 balls to spare.

But Carey was adamant the defeat didn't sap the spirit of Australia, who have lost seven in a row amid 17 losses in their past 19 ODIs.

"We're really confident still, obviously the conditions were quite tough over there but that's no excuse," he said.

"The work we're doing off the field with JL (coach Justin Langer) and the players coming in, we're doing so much good stuff and it's going to start to show.

"We're really confident that its going to turn really soon.

"We don't feel under pressure internally ... we obviously want to win, that's what we're playing for.

"I guess the pressure is to maybe start performing but what we're doing away from game day is sensational, so it's going to turn really quickly."

Australia are likely to alter their line-up for the Adelaide Oval day-night match with spinners Adam Zampa and Ashton Agar in the selection frame.

Both missed the series opener as the hosts plumped for a four-pronged pace bowling brigade on the fast Perth pitch.

"In all short formats, spin is a key contributor," Carey said.

"If it's Zampa, if it's Agar, if it's the same four quicks, I definitely think we have got the bowling attack to go through South Africa.

"Obviously the batters, hopefully, get a few more runs on the board.

"But Adam Zampa (on his) home deck, I'm sure he's really excited and hopeful to be in the side."

Australian Associated Press