The action by the rating agency comes on the heels of the second bailout of the debt-burdened country, calling on its private creditors to write off its debt.
Fitch said the announcement acknowledged a common understanding had been reached between Greece and the private sector on the general terms of a private sector involvement exchange offer, including a nominal haircut of 53.5 percent to the face value of Greece's government bonds.
Fitch said the exchange, if completed, would constitute a "distressed debt exchange."
"The sovereign IDR (issuer default ratings) has accordingly been lowered to 'C' from 'CCC' indicating that default is highly likely in the near term. The ratings of the securities subject to the exchange have also been lowered to 'C' from 'CCC,'" the agency said.
The agency said it will further lower Greece's rating to ''Restricted Default'' status when the debt waivers are completed.
"Shortly after completion of the exchange with the issue of new securities, Greece's sovereign rating will be moved out of the 'RD' category and re-rated at a level consistent with the agency's assessment of its post-default structure and credit profile," the announcement said.