Moritz Kraemer told Reuters that although the firm's longer-term base case remained that Greece would end up leaving the euro, the deal had reduced the immediate risk of that and could lead to an upgrade from its CCC- grade in the next week or two.
"It could happen pretty quickly," Kraemer said. "If you have a solid programme that we think is conducive to bringing growth back to the economy and allowing the financial system to work again, then this is more important than the medium-term debt sustainability question."
(For factbox on euro zone sovereign ratings click)
A key issue now for Kraemer and S&P is whether the Greek government can push the deal through parliament without losing its majority, a move that would force it to either step aside or reshape.
But while the euro zone's bitter negotiations had tarnished the bloc's image, Kraemer said S&P would not start automatically factoring in a premium for a risk that any country could now potentially leave the euro.
"No I don't think we do (have to systematically factor in national currency re-domination risk)," Kraemer said. "I think Greece is not only rating-wise but also other respects in a league of its own in the euro zone.
"We have made no change in our Grexit probability although the timeframe may have been lengthened."
(Reporting by Marc Jones; Editing by Ruth Pitchford)
By Marc Jones
