EBay on Tuesday rejected GameStop 's $56 billion takeover proposal, calling the unsolicited bid "neither credible nor attractive." GameStop CEO Ryan Cohen last week unveiled an audacious bid for eBay, offering to acquire the online marketplace for $125 per share in a cash-and-stock deal. EBay is much larger than the video game retailer, with a market cap of just over $48 billion, while GameStop's is roughly $10.3 billion. "The Board, with the support of its independent advisors, has thoroughly reviewed your proposal and has determined to reject it," Paul Pressler, the chairman of eBay's board, wrote in a letter . "We have concluded that your proposal is neither credible nor attractive." GameStop didn't immediately respond to a request for comment. EBay listed several concerns with GameStop's offer, including "the uncertainty regarding your financing proposal," along with operational risks and the debt load that would result from the proposed transaction.…