If Onions is not fit, his Durham team-mate Steve Harmison could come into the reckoning after taking 6-20 in 13 overs to help his county to an innings victory over Nottinghamshire last week.
BBC: I can complete series - Flintoff
2.
The teams face each other again in Johannesburg next week, with the hosts now out of the Tri-Nations reckoning after a fourth defeat in five matches.
BBC: South Africa 15-27 Australia
3.
Graeme Dott is out of the reckoning after losing 4-0 to Anthony Hamilton, his third successive defeat, while world champion and world number one John Higgins cruised to a 4-0 win over Mark King.