The third director in a week has resigned from Kodak Co as the former film giant struggles to cope with the dominance of digital photography.

Laura Tyson, a professor and former White House economist, told Kodak on Thursday she was resigning from its board, the company said on Friday in a Securities and Exchange filing.

Speculation flared in September that Kodak was on the verge of bankruptcy after the Rochester, New York-based company hired restructuring experts.

Last month, Kodak warned that unless it could raise $500 million in new debt or sell some patents in its portfolio, it might not survive 2012.

Earlier this week, the company said directors Adam Clammer and Herald Chen had resigned.

Clammer and Chen were representatives of private equity firm KKR & Co and had joined Kodak's board in 2009, after KKR bought $300 million of Kodak's senior secured notes and warrants to buy 40 million of the company's shares.

Kodak's shares edged lower in extended trade to 63 cents after closing marginally down at 65 cents.

(Reporting by Sinead Carew; Additional reporting by Noel Randewich in San Francisco; Editing by Gary Hill and Gunna Dickson)