Shares of Citigroup, the largest U.S. bank, fell 2.4% before the bell Monday, after it said it expects to report a decline of about 60% in third-quarter net income, which its chief executive called "a clear disappointment."
Other U.S. banks' shares also took a hit after Citi's statement, which underlined investor worries about fallout from the collapse of the U.S. subprime mortgage market.
JPMorgan Chase shares fell 0.9% to $45.39 before the opening bell, while Bank of America slipped 0.7% to $49.90.
Shares of Citigroup dropped to $45.56 from Friday's close of $46.67.
Financial shares in Europe had already been under pressure, after two major Swiss banks that said they had been hit by credit market volatility. UBS forecast a quarterly loss, while smaller rival Credit Suisse said its profit would fall sharply.