Greece is facing an increasing likelihood of default, even if creditors reach an agreement on a deal aimed at reducing the nation's massive debt load.
Speaking at a Bloomberg sovereign debt conference in New York Tuesday, John Chambers, head of sovereign ratings at S&P, said Greece's debt burden is still "very high" and the nation's credit rating will remain "very low."
Even with the writedowns being discussed, any deal between Greece and private sector investors would "in all likelihood" qualify as a default, Chambers said.
The aim of the deal is to slash the nation's debt load to 120% of gross domestic product by 2020 from its current 160%. Last week, officials from the European Union, International Monetary Fund and European Central Bank were in Athens to review Greece's finances and start negotiating a second bailout.
Greece is facing a €14.5 billion bond payment in March that it may not be able to make without another injection of emergency financing.
However, a downgrade may not come for several months. Chambers said the ratings agency isn't expected to lower Greece to a "selective default" rating until the fall.
Greek debt deal hinges on interest rate impasse
A default could force Greece out of the euro currency union, which would most likely cause the Greek banking system to collapse and plunge the nation's economy deeper into recession.
Economists worry that could start the spread of deeper debt contagion in the eurozone but Chambers disagreed.
"It's not a given that Greece's default would have a domino effect in the eurozone," he said.
Jose Manuel Gonazalez-Paramo, a member of the ECB executive board, downplayed concerns about a default. He said simply "a default should not happen."
On the restructuring, Gonzalez-Paramo said "my impression is that we are close to the end of theses negotiations." He added that the ECB is not directly involved in the talks, but said he's hopeful "that common sense will prevail."