Volkswagen, the market leader in China with a 35 percent market share, would be especially hard hit if growth forecasts for the booming Chinese market prove to be wrong.
Hyundai/Kia and Nissan are the manufacturers with the most aggressive investment plans.
"The huge excess in capacity is the main reason to worry," said S&P expert Maria Bissinger.
By 2010 total capacity is forecast to increase to eight million units a year up from the current two million cars produced.
Further factors causing insecurity are legal uncertainties and a tax system that makes it unattractive to transfer profit to a company's home market.