Eurozone leaders agreed a string of measures designed to finally get on top of the bloc's debt crisis last week, including using joint funds to support Spain's banks, removing a clause that which gave the bloc's bailout fund priority over other bond holders and giving the ECB new supervision powers.
"The tide may be turning for eurozone sovereigns following the June 29 summit," S&P said in a report. "These agreements could help to stabilise the eurozone and staunch any further weakening of sovereign creditworthiness."
But because S&P said it saw a substantial risk that the agreements may not be put into practice. It left its eurozone ratings unchanged and warned it further cuts could be on the cards if promises were not followed through.
"We could take broader rating actions if we see recidivism on the measures agreed to at the June 29 summit," S&P said.
Rating agencies broadly welcomed last week's decisions.
DBRS said on Monday that the deal could be positive for Spain's banks, possibly sparing the country a rating cut that would trigger additional collateral at the ECB.
S&P and its peers Moody's and Fitch have repeatedly stirred market tensions during the European debt crisis with their downgrades of eurozone member states.