"I wish I could borrow more," Chanos told CNBC on Thursday.

Investors who take short positions borrow stock, then sell the shares in hope of being able to buy back shares at a lower price later, allowing them to pocket any difference in price once the shares are returned to the lender.

But if a stock surges, as in the case of SolarCity, a short seller's losses can climb rapidly, making it too risky to hold on even if the investor still believes the stock price will eventually collapse.

Chanos asserts that SolarCity, a provider of solar energy systems, is burning $500 million per quarter.

SolarCity sells most of its solar panel systems via lease deals. Chanos has said that the lease system is akin to taking out a second mortgage on a home.

When Chanos announced on Aug. 21 that he was short SolarCity shares, they fell as low as $40.75 before closing at $40.99. The stock continued to fall, dropping by 39 percent until it bottomed on Nov. 11 with a $25.07 close.

SolarCity shares are now up 22 percent from when Chanos first announced his short position. On Thursday they closed up 6.6 percent at $57.26.

(Reporting by Jennifer Ablan and Lewis Krauskopf; Editing by Leslie Adler)