Two in five millionaire investors see the European debt crisis as a major factor in the economic problems facing the U.S. and consequently are adjusting their investment strategies, according to a survey released by Chicago-based the Spectrem Group.

Twenty-three percent of Spectrem's millionaire survey respondents say they are avoiding individual stocks and mutual funds with a global exposure. And more than 18 percent say they are avoiding fixed-income products from other countries.

Millionaire investors appear to be significantly more concerned about the effects of the European debt crisis than investors at the other end of the wealth spectrum. The debt crisis is perceived as significant U.S. economic problem by only 22 percent of investors who have a net worth of less than $100,000, not including primary residence.

Spectrem Group predicts that those millionaire investors are likely to return to international investing once the global economy stabilizes. A small share of millionaire investors -- about 4 percent -- has increased their exposure to international products due to high yields and attractive prices.