The head of Standard & Poor's sovereign ratings, David Beers told Fox News Sunday he did not expect that much impact when global markets open on Monday due to what he called a mild deterioration in the U.S. credit standing to AA-plus from top-tier AAA.

Asked about the prospects for a further lowering of the U.S. rating, Beers said, the agency's negative outlook meant that risks are on the downside.

He also said the downgrade announced on Friday was not due to the budget positions of any political party and that on any future agreement, We think credibility would mean any agreement would command support from both political parties.

Beers called the U.S. Treasury Department's criticism of the credit rating agency's analysis a complete misrepresentation. Even with the debt limit agreement passed by Congress, he said, the underlying debt burden of the U.S. is rising and will continue to rise over the next decade.