U.S. stock index futures pointed to a lower open on Monday as renewed concerns about the euro zone sovereign debt crisis overshadowed the lift from several large acquisitions.

Pressure grew on Portugal to seek financial help from the European Union and International Monetary Fund, though the European Commission on Monday denied that discussions were underway on an EU/IMF bailout.

Duke Energy Corp agreed to buy Progress Energy Inc

for $13.7 billion in stock, and DuPont

plans to buy Danisco , a Danish food ingredient firm, for $5.8 billion.

Shares of Progress slid 1.5 percent to $44.05 in premarket trading, and Duke fell 1.6 percent to $17.50. DuPont, a Dow component, fell 1.5 percent to $49.02.

While it's always encouraging to get deals of this size, since it suggests confidence is coming back, we still don't know how much downside we could see from the Europe situation, said Michael O'Rourke, chief market strategist at BTIG LLC in New York.

A group of private equity firms, including Apollo Global Management , is interested in buying Sara Lee Corp and has approached the company, a source said. Sara Lee rose 5.6 percent to $18.40 before the bell.

S&P 500 futures fell 5.2 points to 1,262.50 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 slid 41 points and Nasdaq 100 futures lost 6.5 points.

The S&P 500 is finding support at its 14-day moving average, which is around 1,260. Last week the Dow and S&P notched a sixth straight week of advances, while the Nasdaq rose 1.9 percent.

Alcoa Inc is scheduled to report its quarterly results after the market closes, unofficially launching the fourth-quarter earnings season. The stock, a Dow component, edged 1.1 percent higher to $16.60 in premarket trading.

February crude futures rose 0.6 percent to $88.58 per barrel after the Trans Alaska Pipeline was shut because of a leak, sparking concerns about how U.S. supply could be impacted.

U.S. stocks fell on Friday after a court ruling in a key foreclosures case prompted investors to pull out of bank stocks, adding to weakness after a lackluster jobs report.

Portugal