US stocks seen down ahead of budget deficit data

U.S. stock index futures signaled a lower open on Monday, after weaker-than-expected gross domestic product (GDP) data from Japan.

The Japanese Nikkei fell to a six-week low after second-quarter GDP came in at an annualized rate of 2.6 percent, lower than market forecasts of a 3.6 percent gain. However, Japanese officials said the data highlighted the success of "Abenomics", as it marked a third straight quarter of expansion.

Meanwhile, the Shanghai Composite rallied to a 7-week high after a key measure of China's money supply showed a 14.5 percent increase in July on the previous year, and new bank loans grew better than expected.

The data, released late Friday, was the latest sign of a rebound in China's economy, following last week's upbeat industrial production numbers.

In Europe, Greece posted a second-quarter GDP contraction of 4.6 percent year on year, narrowly better than the 5 percent decline analysts had forecast.

Meanwhile, the U.S. Treasury will release details of its budget deficit for July at 2 p.m. ET. Plus, the Federal Reserve will purchase between $1.25 billion and $1.75 billion of 23-30 year Treasury notes.

"We look for the U.S. federal government to have posted a budget deficit of $96 billion in July, which would bring the deficit to $606 billion for the first 10 months of the fiscal year," said Barclays analysts Rahul Bajoria and Laurent Fransolet in a research note.

Monday will be a quiet day for second-quarter earnings reports, with numbers due from Icahn Enterprises and Sysco before Wall Street opens.

Stock of General Motors will also be worth watching on Monday, after weekend media reports suggested the U.S. automaker was cutting its presence in South Korea, amid mounting labor costs and militant unionism.

By CNBC's Katy Barnato