Rating agency Fitch downgraded Greece's long-term foreign and local currency Issuer Default Ratings (IDRs) to "C" from "CCC" on Wednesday, said a statement.
Moreover, the statement said it now considered that a Greek debt default was "highly likely in the near term."
Fitch also affirmed Greece's short-term foreign currency rating at "C", adding that the euro area ceiling at "AAA", which is applicable to all eurozone member states.
The downgrade followed Eurogroup's statement on a second financing programme for Greece including "private sector involvement" (PSI) and a subsequent announcement from the Greek authorities outlining the terms of the proposed exchange of Greek Government Bonds (GGBs).
The downgrade is in line with Fitch's statement on 6 June 2011, which outlined its rating approach to a sovereign debt exchange.