South Australian Opposition Leader Isobel Redmond has quit the Liberal leadership because of party disunity, setting up a vote to replace her.

Current deputy leader Steven Marshall will reveal on Friday if he will be a candidate, while former foreign minister Alexander Downer has ruled himself out.

The party-room ballot is expected on Monday.

Another potential candidate is former health spokesman Martin Hamilton-Smith, who challenged for the leadership late last year but lost a ballot 13 votes to 12.

Ms Redmond said she had been privileged to lead the state Liberal parliamentary team for the past three and a half years.

"However, in the face of ongoing leadership speculation and disunity I have reached the conclusion that it is in the best interests of the Liberal Party if I step aside," she said.

"Whoever is chosen as the new leader has my guarantee of my loyalty and support."

Premier Jay Weatherill said Ms Redmond had been undone by a "treacherous and deceitful" campaign from within her own party.

He said the Liberals were riven by factional disputes and all of the leadership candidates had been part of the process to undermine her.

"They have achieved their ultimate goal, which is to force her to resign," Mr Weatherill said.

Mr Marshall said he would discuss his position with his parliamentary colleagues before making a decision on whether or not to stand.

Mr Downer told reporters in Canberra he still had no intention of returning to politics.

"They will choose a new leader, presumably early next week. I won't be a candidate," he said.

"I'm not a member of state parliament and have no plans to join state parliament."

Federal Opposition Leader Tony Abbott said the leadership was up to the South Australian Liberals.

He said Ms Redmond had done a good job as Liberal leader in SA and had actually won the popular vote at the last state election.

"It was only by some electoral malfeasance in a couple of seats that the Labor Party was able to fall over the line," he said.