The U.S. stock index futures point to a lower open Wednesday as market sentiment continue to be weighed down by fears of the mounting debt pressure faced by the euro zone as Spain has not yet sought help to reduce its borrowing costs.

The futures on the Dow Jones Industrial Average were down 0.23 percent, the futures on the Standard & Poor's 500 Index were down 0.19 percent and those on the Nasdaq 100 index were down 0.17 percent.

Automatic Data Processing will release its National Employment Report Wednesday. The report is a measure of the monthly change in nonfarm private employment data based on the payroll data of approximately 400,000 U.S. business clients. It is expected to rise by 143,000 jobs in September, down from 201,000 in August.

The Institute for Supply Management’s (ISM) non-manufacturing Purchasing Managers’ Index (PMI) will also be reported Wednesday. The ISM non-manufacturing index, which rates the relative level of business conditions, including employment, production, new orders, prices, supplier deliveries and inventories, is expected to fall to 53.2 in September, down from 53.7 in August. A level above 50 represents expansion in the industry.

On Tuesday, the U.S. markets were mixed as investors maintain a watchful mode amid the continuing concerns about the weakening global economic growth. The Dow Jones Industrial Average fell 0.24 percent, the S&P 500 Index was up 0.09 percent and the Nasdaq Composite Index advanced 0.21 percent.

European markets fell Wednesday as investor sentiment remained negative with Spain not so far formally requesting the bailout funds, which in turn would trigger the European Central Bank peripheral bond purchases. London's FTSE 100 was down 23.01 points, Germany's DAX 30 index fell 25.08 points and France's CAC 40 declined 12.30 points.

Stock markets in China and South Korea were closed Wednesday for holiday. Other Asian markets were mixed as investor confidence was weighed down to know that China's non-manufacturing activity declined in September compared to that in the previous month, increasing the concerns over a slowdown in the economic growth of the country. According to data released Wednesday by the National Bureau of Statistics and China Federation of Logistics and Purchasing, the non-manufacturing Purchasing Managers' Index fell to 53.7 in September, down from 56.3 in August.