American International Group Inc shares fell on Wednesday as investors grew increasingly nervous before third-quarter earnings were reported after the close and a takeover premium evaporated.

AIG shares tumbled $4.10, or 6.6 percent, to $57.95 in New York Stock Exchange trading, near their 52-week low of $56.37.

Investors were concerned that AIG, the world's largest insurer, may report big losses from subprime exposure, as several investment banks already have. AIG also has units that are directly involved in lending, such as its United Guaranty mortgage division and its consumer finance arm.

In addition, investor optimism that former AIG Chief Executive Maurice Hank Greenberg would force the company to adopt a strategic alternative, such as selling pieces of the company, has declined, an analyst said.

The Greenberg premium has evaporated, said Donald Light, an analyst with Celent LLC.

Sources said on Tuesday that Greenberg, who in a filing with the U.S. Securities and Exchange Commission last week announced he was talking to other investors, had declined to answer questions about himself when he was deposed by the SEC in September.

The SEC is investigating allegations that Greenberg. who ran AIG for more than 30 years, manipulated earnings at the insurer. Through a spokesman Greenberg declined to comment.

UBS analyst Andrew Kligerman said in a report on Wednesday that he thought the market was overly pessimistic about subprime losses at AIG, and the stock's recent decline represented a good buying opportunity.