Ratings agency Standard & Poor's has downgraded the EU bailout fund to AA+ from AAA.
The European Financial Stability Facility's (EFSF) rating is based on the ratings of the countries that guarantee it.
Following S&P's downgrade of France and Austria on Friday, there were not enough AAA rated guarantors for the fund to maintain its top rating, the BBC reports.
The EFSF was set up to allow countries with top credit ratings to borrow money cheaply that they could then lend to struggling countries. This latest downgrade could affect the EFSF's ability to raise money cheaply.
S&P said the EFSF could regain its AAA rating if it obtained additional guarantees. Alternatively, the fund could be endowed with less money, which would be better guaranteed.
S&P cut its ratings for France, Italy, Spain, Cyprus, Portugal, Austria, Slovakia, Slovenia and Malta late on Friday.
The downgrades took away two of the EFSF's six AAA rated guarantors. This reduces the fund's AAA rated guarantees from 440bn euros ($557bn; £364bn) to about 260bn euros.
European Central Bank President Mario Draghi said yesterday that investors had largely priced in the eurozone downgrades and questioned the importance of ratings companies.
"I will never comment on ratings as such, but certainly one needs to ask how important are these ratings for the marketplace overall, for investors?" Draghi said.
"It seems to a great extent markets have anticipated these ratings changes and priced them in. We should learn to do without ratings, or at least we should learn to assess creditworthiness with less reliance on the ratings companies," he said.
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