The big Boks lock was Man of the Match on the strength of scoring two tries in Ireland's 17 - 31 defeat at Bloemfontein last week.
But on learning of his 11th hour withdrawal, O'Sullivan said: I can't image that the Sprigboks will be appreciably weakened by it. Whoever comes in will be there to do a job. We've lost Gordon Darcy but we just get on with it in pretty much the same way.
The Irish coach also emphasises that Ireland will not be given any advantage if, as predicted, the good sunny weather of midweek gives way to rain. If it rains, both teams will be disappointed. It will then be a case of which team adjusts best to the conditions. The surface is fantastic. It is in pristine condition. It's a great stadium.
Ireland captain, Brian O'Driscoll says there is still a major job to be done in Ireland's 15th Test of the season.
Everyone is up for it. We are all in the zone. We want to end on a high note and take our holiday after - but nobody is thinking of holidays just yet.
It would be huge for us to win. This is a massive opportunity. We let slip an opportunity last week. If we get our game right, we will be there, thereabouts. That's what our focus is about.
