The South African Chamber of Commerce and Industry (SACCI) said its BCI declined from 90.5 in August to its lowest level since September 2003.
A banking crisis in the United States and Europe has sparked a flight from risky assets across the world and fears of a slowdown in global growth.
"Although most emerging economies are not directly exposed to the global financial crisis to the extent that advanced economies are, the contagion effects of recessionary conditions will be realised through international trade and financial flows," the SACCI said in a statement.
"As global investors become more risk averse and financial conservatism features more prominently, the flow of capital to emerging markets is likely to decline."
IT holding company Allied Electronics gave one of the first concrete indications the crisis will hit growth in South Africa earlier on Tuesday, saying it had halted an acquisition drive and would focus on consolidation.
South African businesses and consumers are also trying to cope with high domestic interest rates.
The central bank lifted its repo lending rate by 5 percentage points to 12 percent between June 2006 and June 2008 to tame inflation, before leaving rates steady in August.
It is widely expected to keep the repo unchanged on Thursday, before cutting rates in 2009.