The loss of the AAA rating by Standard & Poor's a month ago was a blow for President Sarkozy as he prepares to seek re-election in April.
At the time, the president reacted to the downgrade by Standard & Poor's by making reference to Moody's greater importance.
"On Monday, another agency, twice as important, said the opposite," he said.
The other agency was Moody's, which had said it was keeping France on a "stable" outlook.
However, on Monday the same agency changed that outlook to "negative", meaning the risk of downgrade was greater.
There may have been some cheer that, on this occasion, France was joined by the United Kingdom in getting the downgrade warning.
In December, a war of words started after the head of the French central bank claimed the UK should be downgraded before France.
"They should start by degrading the United Kingdom, which has greater deficits, as much debt, more inflation and less growth than us," Christian Noyer told regional newspaper Le Telegramme.
Finance minister François Baroin joined in the attack by saying "the economic situation in Great Britain is very worrying" and "we prefer being French rather than British on the economic front at the moment."
Baroin reacted to the latest downgrade threat on Monday saying the government had "noted" the decision.