Stock futures pointed to a lower open on Tuesday after it was reported the International Monetary Fund was set to forecast toxic assets on the balance sheets of financial sheets could reach $4 trillion.

The report comes on the heels of comments from veteran analyst Mike Mayo, of Calyon Securities, who said on Monday banks still face fallout from excessive risk-taking and warned of rising loan losses by the end of 2010.

Bank of America tumbled 3.6 percent to $7.21 in premarket trade, while Citigroup dropped 4.4 percent to $2.60. The renewed worries about banks came after stocks rallied off 12-year lows in the last month, fueled in part by reassuring comments from major banks about their performance in the beginning of the year.

The real jitters here for the market is the report from the IMF suggesting that toxic debts could actually spiral to $4 trillion, said Peter Cardillo, chief market economist at Avalon Partners in New York.

You had some negative analyst reports yesterday on the banks and this IMF report certainly is not helping. It just basically is reopening old worries.

S&P 500 futures fell 14.40 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures slid 123 points, and Nasdaq 100 futures shed 18.25 points.

Jitters over the banks is compounded by worries over the earnings season which kicks off after the close as investors braced for aluminum producer Alcoa's quarterly results.

Alcoa shares fell 2.4 percent in premarket trade ahead of the release of their results.

Earnings for S&P 500 companies are expected to fall by 36.7 percent, according to Thomson Reuters data.

Shares of Microsoft may move higher after RBC Capital Markets upgraded company to outperform from sector perform along with seven other software companies, citing more reasonable valuations and a decreased risk to negative earnings revisions.

Also on the research front, American Express was upgraded to a hold from a sell at Citigroup on a more balanced risk to reward basis.

In Europe, shares fell for a third consecutive session as financials weakened along with U.S. futures, reigniting fears over the global banking sector

In acquisition news, about half a dozen investment managers have put forward bids, ranging from $400 million to $800 million for troubled insurer American International Group's asset management business, the Wall Street Journal reported.

Since hitting a bear market closing low on March 9, the S&P 500 is up more than 23 percent, boosted by hopes that the economic slump is moderating and banks are stabilizing as policy-makers continue an aggressive campaign to shore up the system.

The recent momentum in financials and sectors such as technology, which analysts say may lead a recovery, helped the Dow rack up its best four-week stretch since 1933 despite yesterday's decline.

(Reporting by Chuck Mikolajczak; Editing by Theodore d'Afflisio)