Standard & Poor's is set to downgrade the credit ratings of several eurozone countries later on Friday, but not those of Germany and the Netherlands, a senior euro zone government source said.
The source did not say which or how many other countries' debt ratings would be downgraded. Another source confirmed "several" countries would be hit.
"Remain alert tonight when U.S. markets close," said another eurozone source.
In December, S&P placed the ratings of 15 eurozone countries on credit watch negative - including those of top-rated Germany and France, the region's two biggest economies - and said "systemic stresses" were building up as credit conditions tighten in the 17-nation bloc.
Since then, the European Central Bank has flooded the banking system with cheap three-year money to avert a credit crunch.
At the time, S&P said it could also downgrade the eurozone's current bailout fund, the EFSF.
The ratings agency said that if a downgrade did materialise, countries such as Germany, Austria, Belgium, Finland, the Netherlands and Luxembourg would likely see ratings cuts of only one notch.
The other nine countries - most notably triple A-rated France - could suffer downgrades of up to two notches.
S&P declined to comment on Friday on the Reuters report of an impending wave of downgrades, which hit stocks, the euro and boosted demand for safe-haven U.S. government debt.
A downgrade could automatically require some investment funds to sell bonds of affected states, making those countries' borrowing costs rise still further.
"It's been priced in for several weeks, but the market had been lulled into complacency over the holidays, and the new year began with a bounce in risk appetite, thanks partly to a good Spanish auction," said Samarjit Shankar, Director Of Global Fx Strategy at BNY Mellon in Boston.
"But the Italian auction brought us back to earth and now we face the spectre of further downgrades."
Italy's three-year debt costs fell below 5 per cent on Friday but its first bond sale of the year failed to match the success of a Spanish auction the previous day, reflecting the heavy refinancing load Rome faces over the next three months.