• eBay has rejected Ryan Cohen's $55.5 billion takeover offer.
• The GameStop CEO made an unsolicited offer earlier this month.
• eBay's chairman said the offer is "neither credible nor attractive."

eBay has turned down Ryan Cohen's unsolicited offer to take over its business.

The online marketplace giant said Tuesday that it has officially rejected the GameStop CEO's $55.5 billion bid for the company.

"We have concluded that your proposal is neither credible nor attractive," eBay's chairman wrote in a letter to Cohen.

"We have taken into account such factors as 1) eBay's standalone prospects, 2) the uncertainty regarding your financing proposal, 3) the impact of your proposal on eBay's long-term growth and profitability, 4) the leverage, operational risks, and leadership structure of a combined entity, 5) the resulting implications of these factors on valuation, and 6) GameStop's governance and executive incentives," he added.

This is a developing story.