Kolisi injured his knee playing for the Stormers in Super Rugby and was initially ruled out for six weeks in late May, though it now seems likely his rehabilitation will take longer.
"Van Staden has been drafted in as cover for Siya Kolisi and will remain in camp until there is absolute clarity about whether Kolisi will be able to take part in the initial stages of the Rugby Championship," South African Rugby said in a statement.
"Kolisi is continuing with his rehabilitation in camp."
Van Staden, 23, has two test caps, earned in home wins over Argentina and Australia last year.
The Springboks host Australia in the tournament opener in Johannesburg on July 20 before travelling to Wellington to face New Zealand a week later.
Their final fixture in a shortened Rugby Championship season will be against Argentina in Salta in Aug. 10. The side will also host Argentina in a one-off test in Pretoria a week later before they head to Japan for the Rugby World Cup, which starts on Sept. 20.
South Africa have been grouped with defending champions New Zealand, Italy, Namibia and Canada.
(Reporting By Nick Said; Editing by Peter Rutherford)
