The 30-year-old South African, who was released by Bolton in the summer, has been training with them for a month.
"He's building up his fitness after an operation, but there'll be more news on that over the weekend," manager Roy Keane told the club website.
If he does sign he will become their second signing of the transfer window after Jonny Evans joined on loan.
Speaking after Evans' arrival from Manchester United, Keane said there would be more new arrivals on their way.
"I'm certainly not getting into a panic situation, far from it," he told the club website.