Bank woes bring out the bears

LONDON (CNNMoney.com) -- U.S. stock futures were weaker Wednesday, as investors grew uncertain ahead of Merrill Lynch's earnings.

Concerns that Merrill (Charts, Fortune 500) may suffer a bigger loss than initially estimated due to risky mortgage bets weighed on sentiment. Merrill is due to report its results before the market open.

A little more than two weeks ago, Merrill Lynch said it expects to take about a $5 billion writedown, due largely to this summer's subprime crisis.

But the bank's hit could actually be much higher, at around $7 billion to $7.5 billion, according to reports in the Wall Street Journal and New York Times.

A wider-than-expected loss is likely to renew credit worries and further depress shares in the banking sector.

In the tech sector, Amazon.com (Charts, Fortune 500) reported late Tuesday a surge in quarterly sales and earnings. But investors expressed disappointment with the results, sending the online retailer's shares lower in after-hours trading.

In global trade, stocks in Asia gave up their gains and European markets were lower in early trading.