The indestructible fast bowler, now 36, with 103 Tests and 375 wickets to his name, is being treated for tendonitis in his left knee.
His status was transformed from a 75 per cent chance to be ready for the Test to a near-certainty when captain Brian Lara revealed that leg-spinner Dinanath Ramnarine's unfit bowling shoulder would rule him out of the match and probably the tour itself.
Walsh, two wickets away from surpassing team coach Malcolm Marshall's West Indies record number of Test wickets, bowled off a shortened run during open team practice in the middle of Springbok Park immediately following the team's defeat by Orange Free State just over half-hour into the final day yesterday.
Unlike Ramnarine, Lara said he would depend on Walsh himself to report whether he was fit enough for a Test.
``If you're going to play in a Test match, you want to know you're capable of handling it,'' he said.
``It's a different story with Courtney Walsh (than with Ramnarine). He's been around for 100-odd Test matches and I think we can get a truer picture from that individual when the time comes.''
Walsh has missed only one Test through injury in a career that started exactly 14 years ago against Australia in Perth. He has repeatedly disregarded injuries of one sort or another to take his place.