Following an investigation by Diamond Food's board of directors' audit committee, the snack foods group also said it had fired chief executive Michael Mendes and chief financial officer Steven Neil, effective immediately.

P&G said Thursday it is placing the deal, announced on April 5, under evaluation in light of the announcement. P&G on its website described the revelation as "very disappointing" and said it needs to consider its next steps as it is "keeping all our options open."

Though P&G wouldn't comment specifically, one of those options could be to assert a material adverse change. A MAC is a clause typically placed in takeover agreements that allows a buyer to walk away if a material adverse change happens to the target company during the time a deal is announced and completed.

Terms of the agreed deal called for Diamond Foods to issue 29.1 million shares, worth $1.5 billion, and assume about $850 million in Pringles debt. Because Diamond Food is paying for the deal in stock, P&G and its shareholders have a vested interest in Diamond Foods' financial performance. As a result, P&G could attempt to assert a MAC clause even though Diamond Foods is not the target, but the buyer.

San Francisco-based Diamond Foods did not respond to requests for further comment.

In an e-mail, Cincinnati-based P&G's corporate communications director, Paul Fox, said it was premature to discuss specific actions. "We will evaluate yesterday's disappointing news from Diamond Foods and align [our] appropriate next steps," he said. "We are keeping all our options open."

Fox said there is no time frame for the evaluation process, but the transaction will expire if it is not completed before June 30.

Investors on Thursday punished Diamond Foods stock, sending shares down nearly 37% to close at $23.13. The stock traded as high as $92.47 per share on Sept. 20.

Diamond Foods' audit committee found that a "continuity" payment made to growers in August 2010 of about $20 million and a "momentum" payment made in Sept. 2011 of nearly $60 million were not accounted for in the correct periods. The company will now include the $60 million payment in its 2011 fiscal results, and the $20 million payment will be shifted from Diamond Food's 2011 financial results to 2010.

The charges are indeed material, as Diamond Foods earned a total of $50 million in 2011 and $26 million in 2010.

As Diamond Foods searches for a new CEO and CFO, director Rick Wolford will serve as acting CEO and president. Michael Murphy, a managing director of Alix Partners LLP, will serve as acting CFO. Robert Zollars, CEO of Vocera Communications Inc., has been appointed chairman of the board.

Wolford was previously chief executive of Del Monte Foods Co. and has been a director of Diamond Foods since April 2011. Diamond Foods' brand portfolio consists of Kettle Chips, Emerald snack nuts, Pop Secret popcorn and Diamond of California nuts.