Controversial investor Carl Icahn's shares in Yahoo have fallen nearly $950m in value since he took a $1.8bn stake in the internet firm.
Securities and Exchange Commission figures show Icahn paid an average of $23.59 a share for his 5.5% stake in Yahoo.
But shares closed yesterday at $11.05, which means they will have to more than double in value before Icahn could make a profit, according to the Washington Post.
Yahoo's value has dropped more than $30bn since the company rejected a Microsoft buyout offer of $33 a share in February.
Icahn bought Yahoo shares in an attempt to oust Yahoo's board of directors and reach a deal with Microsoft, but settled for a directorship when his bid failed.
The investor is still holding out for Microsoft to take over Yahoo's internet search operations.
Share prices had rallied on hopes of a Microsoft deal after Yahoo announced plans to replace Jerry Yang as chief executive, but fell again after Ballmer ruled out the possibility.
Icahn said on US television this week he believes Yahoo is undervalued, indicating that he still hopes to recoup his investment, against the odds.