Ahead of the opening bell, Dow Jones industrial average futures are down 97, or 0.8 percent, at 12,369. S&P 500 index futures are down 10, or 0.8 percent, at 1,317. Nasdaq 100 futures are down 20, or 0.8 percent, at 2,324.
Ratings agency Standard & Poor's cut its outlook Saturday on Italy's debt to negative from stable.
Financial markets in Spain are down sharply after a defeat for its ruling Socialist party caused investors to fear that the government cannot solve its public finance issues.
On Friday, the Fitch ratings agency downgraded Greece's debt rating further into junk status.