U.S. stock index futures were sharply lower on Friday, a day after markets were shut for the U.S. Thanksgiving holiday, as a possible debt default at a Dubai state-owned conglomerate sparked fears of renewed global financial turmoil.

Dubai, part of the oil-exporting United Arab Emirates, shook the financial world Wednesday when it said it would ask creditors of state-owned Dubai World and builder Nakheel for a standstill agreement on billions of dollars in debt as a first step towards restructuring. 

The U.S. dollar, considered a safe haven for investors, rose 0.7 percent against a basket of currencies, while January crude futures dropped 5.2 percent to $73.96 per barrel.

Overseas markets sank on the news. Hong Kong shares .HSI dropped 4.8 percent, and Shanghai stocks .SSEC fell 2.4 percent. 

U.S.-listed shares of banking and financial services group HSBC Holding (HBC.N)(HSBA.L) fell 7.3 percent to $57.52 in premarket trading.

Markets have been coasting along with the assumption that the wall of worry is behind them. This moves the mindset backwards, said Andre Bakhos, president of Princeton Financial Group in North Brunswick, New Jersey.

Investors everywhere are looking at this and fearing it means we could slide back into an economic crisis.

S&P 500 futures SPc1 sank 30.3 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 DJc1 tumbled 222 points, while Nasdaq 100 futures NDc1 slid 50.25 points.

Investors will closely be watching the results of Black Friday, the unofficial start of the crucial holiday shopping period. Many retailers are offering steep discounts in order to lure in customers with bargains.

Consumer spending accounting for about 70 percent of the U.S. economy, and the strength of Friday's sales could suggest how willing consumers are to spend in the season.

Retailers are going to try and drive their topline with discounting, but discounts weigh on margins and that will put pressure on the bottom line, Bakhos said.

Trading volume will likely be low in Friday's shortened session. No companies are scheduled to report quarterly results and no major economic data is on tap.

In Wednesday's session, stocks rose in light volume as data pointed to stabilization in the labor and housing markets, areas that have fed concerns about a double dip recession.