The blanket warning applies to AAA-rated nations such as Germany, France, the Netherlands, Austria, Finland and Luxembourg, the U.S.-based credit rating agency said in a press release.
But the review does not change anything for two members of the 17-nation monetary and currency union. Greece's credit rating currently reflects a high risk of default, and Cyprus was already under review.
S&P said the review was prompted "by our belief that systemic stresses in the eurozone have risen in recent weeks to the extent that they now put downward pressure on the credit standing of the eurozone as a whole."
The agency sees five factors behind the current debt crisis: Tightening credit conditions, rising yields on bonds issued by top rated sovereigns, ongoing political deadlock over how to deal with the crisis, high levels of government and household debt, and the rising risk that Europe will suffer an economic recession next year.
France is already seen as the most likely candidate to be stripped of its AAA status. But the decision to review Germany, the euro area's most creditworthy nation, points to the severity of the crisis.
Other euro area nations have already seen their ratings slashed by S&P, a division of McGraw-Hill. Most recently, S&P cut its rating on Belgium late last month.
European leaders try again
Italy and Spain have also suffered deep downgrades this year, although both nations retain investment grade ratings. Ireland and Portugal are also clinging onto investment greade ratings, but the rating on the bailed-out nation of Greece is already at junk status. (See correction below)A downgrade of France or another of the region's top rated nations would have serious consequences for the European Financial Stability Facility. The EFSF, a government backed bailout fund, could lose its AAA rating if the nations that stand behind it are downgraded.
Correction: An earlier version of this article incorrectly reported that Ireland and Portugal have already been cut to junk status.
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