U.S. stock index futures fell on Friday, following Wall Street's worst day in more than nine months, as lingering worries over the fiscal health of some European countries curbed risk appetite ahead of a key U.S. jobs report.

The cost of insuring Greek, Portuguese and Spanish government debt rose to record highs Friday on mounting fears about debt defaults. Many investors had their eyes on Portugal, where parliament was to vote on a regional financing bill seen as a crucial test of the government's ability to curb public spending.

We've got ongoing concerns about who the next sovereign debt problem child is going to be. So we're going to see the dollar firm up against the euro and commodities fall off because of that, said Art Hogan, chief market analyst at Jefferies & Co in Boston.

On the U.S. economics front, analysts in a Reuters poll predicted non-farm payrolls grew by 5,000 in January after an unexpected loss of 85,000 in December. The unemployment rate is expected to edge up to 10.1 percent in January from 10 percent. The government report is due at 8:30 a.m.

We may have created jobs for the second time in a year, Hogan said. Unfortunately, this will be overshadowed by major global economic concerns.

S&P 500 futures fell 4.8 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 35 points, and Nasdaq 100 futures fell 1 point.

Aetna Inc posted lower quarterly profit early Friday, missing the average estimate, on high medical costs for its commercial health plans. The big health insurer also forecast 2010 profit below Wall Street's target.

The Obama administration's proposal to limit risk-taking by major banks in the wake of the financial crisis could affect about 10 percent of Goldman Sachs Group Inc's net revenues, a senior company executive told a U.S. Senate committee.

U.S. stocks suffered their worst losses in more than nine months on Thursday on fears over euro zone debt and an unexpected rise in U.S. claims for jobless insurance. The S&P 500 <.SPX> fell 3.1 percent.

(Editing by Jeffrey Benkoe)