The Greek economic crisis is threatening U.S. money markets, long considered safe investments, according ratings agencies.

Forty-four percent of money-market funds in the U.S. are invested in the short-term debt of European banks, according to Fitch Ratings, while Moody's is reporting that 55 percent of those holdings are in the commercial paper of French banks, such as Societe Generale, BNP Paribas and Credit Agricole, according to CNBC.

French banks are some of biggest creditors to debt-ridden Greece, with more than $53 billion in outstanding loans.

The world is watching to see if Greece can avoid defaulting on its sovereign debts, which could send shockwaves through European and U.S. financial sectors.

On a positive note for U.S investors, money-market funds are backed by the U.S. government.

Greece is likely to receive support from the European Union, although the country must accept the tough task of carrying out highly unpopular austerity measures in order to narrow is wide budget gap.

EU's Olli Rehn (Getty Images photo)

Olli Rehn, the EU's monetary affairs commissioner, has said eurozone governments would likely agree on giving Greece the $17 billion as part of a larger lending facility in the coming days.

Yet Europe will insist the country stick with the austerity measures that include unpopular tax hikes, increases to retirement ages, which used to come around the age of 50, and cuts to public-sector payrolls.

"The situation on the Greek street is showing how little room to maneuver there is domestically," says Sony Kapoor, managing director of Brussels-based think tank Re-Define, according to the Associated Press.