"Keeping it would amount to a miracle, but I'd still like to believe it," said Jean-Pierre Jouyet, the outspoken head of the AMF regulation agency.
Ratings agencies have warned that France is exposed to the sovereign debt crisis gripping southern Europe and have threatened to downgrade its hitherto perfect rating.
The government has protested that it has embarked on an austerity programme backed by a pact with fellow eurozone members to guarantee deficit reduction.
"I find it wholly regrettable that we are accepting the loss of our triple-A with a kind of fatalism. This loss is not banal, because it will have an effect on the interest rates the state pays," he said.
He also warned that if France was downgraded it would weaken the status of the European Financial Stability Facility and the European Stability Mechanism, two instruments set up by eurozone leaders to confront the crisis.
Any suggestion that France's debt of €1.7 trillion euros ($2.2 trillion) is becoming unmanageable could send the interest rate it pays on bonds soaring.
Earlier, the French treasury announced that it would need to raise €178 billion ($232 billion) in medium and long-term bonds next year.
The Fitch credit rating agency also warned on Tuesday that the eurozone's new bail-out fund could lose its triple-A debt status.
"Fitch Ratings says the 'AAA' rating on debt issues of the European Financial Stability Facility largely depends on France and Germany retaining their 'AAA' status," the company said in a statement.
"The revision of the rating outlook on France to 'negative' last Friday implies that the risk of a downgrade of EFSF debt has increased," it said.
Last week, Fitch "affirmed France's 'AAA' status but warned that there is a slightly greater than 50 percent chance of a downgrade within the next year or two.
"France is the most exposed of the 'AAA' euro member states to a further intensification of the eurozone sovereign debt crisis," it added.
Another agency, Standard and Poor's, has warned that it is re-examining France's rating and it is expected to announce a downgrade soon.