U.S. banks face a "serious risk" that their creditworthiness will deteriorate if Europe's debt crisis deepens and spreads beyond the five most-troubled nations, Fitch Ratings said.

"Unless the euro zone debt crisis is resolved in a timely and orderly manner, the broad credit outlook for the U.S. banking industry could worsen," the New York-based rating company said yesterday in a statement. Even as U.S. banks have "manageable" exposure to stressed European markets, "further contagion poses a serious risk," Fitch said, without explaining what it meant by contagion.

The "exposures" of U.S. lenders to major European banks and the stressed nations of Greece, Ireland, Italy, Portugal and Spain, known as the GIIPS, are smaller than those to some of the continent's larger countries, Fitch said.