Stocks were set for a lower open on Thursday after a rating agency downgrade of Spain rekindled concerns over euro zone debt problems and disappointing economic data from China and the United states heightened global growth worries.

Futures slid after government data showed initial claims for state unemployment benefits increased 26,000 to a seasonally adjusted 397,000 and the trade deficit widened much more than expected in January to $46.3 billion.

Moody's one-notch downgrade of Spain, based on the costs of restructuring its banks, came with a warning that further cuts were possible. The agency downgraded Greece's debt earlier this week.

China swung to an unexpected trade deficit in February of $7.3 billion, its largest in seven years, but economists said the drop was likely temporary.

The Spain downgrade helped lift the dollar against the euro and pushed oil prices lower, even as Libyan leader Muammar Gaddafi carried counterattacks deeper into the insurgent heartland. Brent crude futures fell 1.2 percent to $114.51.

Overseas issues continue to play a role in U.S. markets. The situation in Europe isn't complete, the market continues to have concerns about sovereign credit, said Subodh Kumar, chief investment strategist at Subodh Kumar & Associates in Toronto.

Markets have been hoping that China would lead the recovery, but when you put this (U.S.) data with slower growth out of China, the idea that everything looks normal is going away.

S&P 500 futures lost 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 fell 54 points, and Nasdaq 100 futures dropped 12 points.

HCA Holdings Inc was expected to begin trading on the New York Stock Exchange after the hospital operator sold more shares than planned in the largest-ever U.S. private-equity backed initial public offering.

Human Genome Sciences Inc jumped 10.3 percent to $28.30 in premarket trade after health officials cleared the company's Benlysta treatment for lupus. Annual global sales might top $3 billion in 2015, according to Thomson Reuters consensus forecasts.

Starbucks Corp is partnering with Green Mountain Coffee Roasters Inc to take on the fast-growing single-serve market. Starbucks gained 8.1 percent to $37.35 and Green Mountain surged 26.7 percent to $53.30 in premarket trade.

(Additional reporting by Ryan Vlastelica; Editing by Padraic Cassidy)