U.S. stock index futures point to a flat opening Tuesday as investor sentiment continue to be affected by the mounting borrowing costs faced by Spain and worsening economic condition of Greece.

Futures on the Dow Jones Industrial Average were down 0.03 percent, futures on the Standard & Poor's 500 index were down 0.05 percent and futures on the Nasdaq 100 index were up 0.03 percent.

Investor sentiment is expected to be affected by the concerns of the economic crisis faced by Greece. Market players are worried about the future of Greece in the euro zone.

Investors sense that the important issue will be for the Troika consisting of the European Commission, the European Central Bank and the International Monetary Fund (IMF) to decide upon what Greece must to do to guarantee that it receives all the planned future loan payments. Given that government revenues remain below their target and the recent deterioration in the economic outlook, the IMF recently warned that Greece would miss its budget deficit goals if there was no further action.

The fears of contagion increased as the 10-year government bond yields in Spain soared to record highs of about 7.56 percent, adding to concerns about the amount of sovereign funding needed.

Also Moody's Investors Service said Monday that it was changing its outlook for Germany, the Netherlands and Luxembourg to negative from stable. It cited the increasing risk of Greece leaving the euro currency and the need for more support required for Spain and Italy as reasons for the change in outlook.

On Monday, the U.S. markets fell as investor confidence was down following increasing debt pressure on Spain and worrying financial situation in Greece. The Dow Jones industrial average fell 0.79 percent, the S&P 500 Index declined 0.9 percent and the Nasdaq Composite Index was down 1.20 percent.

Major European indices rose, but investors remained watchful amid continuing concerns of the economic situation in the euro zone. London's FTSE 100 was up 12.12 points, Germany's DAX 30 Index rose 6.04 points and France's CAC 40 advanced 18.18 points.

Asian stocks made gain as market sentiment was lifted with the report released Tuesday that China's manufacturing activity rose in July compared to that in June, according to the preliminary HSBC Flash Purchasing Managers Index (PMI). The preliminary reading of the PMI, a measure of the nation-wide manufacturing activity, climbed to 49.5 in July compared to 48.2 in June.