DUBLIN (Reuters) - A downgrade of sovereign debt would not necessarily have a big impact on financial markets, billionaire investor Wilbur Ross said.

A late deal could raise the prospect the United States will lose its top-notch triple-A credit rating, which analysts say would rattle financial markets and raise borrowing costs for Americans.

"I am not at all certain that even if they were to downgrade U.S. debt to double-A, it is not at all clear that would have a big impact on markets," Ross told Reuters in a telephone interview late on Friday.

"It depends to what level and how much markets really believed the downgrade," he said. "At the end of the day who decides where paper trades and whether new issues are sellable is the market, not the rating agencies."

He said he expected the crisis to be over by the August 2 deadline after which the Treasury says the government would be barred from further borrowing.

"If the U.S. solves its problem, as I believe and assume that it will, by August 2 ... I think that crisis will be behind us," Ross said. "I really don't see default as such happening."

(Reporting by Conor Humphries; Editing by Catherine Evans)