Standard & Poor's will likely downgrade Greece's ratings to "selective default" when the country concludes its debt restructuring, but that will not necessarily destroy the credibility of the European Union, an official with the ratings agency said on Tuesday, January 24.

"It's not a given that Greece's default would have a domino effect in the euro zone," John Chambers, the chairman of S&P's sovereign rating committee, said in an event organized by Blooomberg Link, Reuters reported.

On Tuesday, eurozone finance ministers pressed Greece to prepare new budget cuts soon and conclude negotiations with bank creditors on a massive debt writedown within days to avoid a messy default. European economic affairs commissioner Olli Rehn urged Greece to accelerate economic reforms in order to spur growth, after talks between finance ministers that began Monday afternoon and ended past midnight.