FORMER foreign minister Alexander Downer has rejected speculation he will seek to fill the vacancy created by South Australian opposition leader Isobel Redmond's resignation.

Current deputy leader Steven Marshall will reveal on Friday if he will be a candidate, but Mr Downer ruled himself out. The party-room ballot is expected on Monday.

Ms Redmond quit yesterday because of party disunity.

Mr Downer said 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.''