Andrew Left, founder of Citron Research and one of the world's best known short-sellers, on Monday described cryptocurrencies as a "fraud."
Asked at a conference about fraud in financial markets where he saw potential fraud, Mr Left told the audience: "I think crypto is just complete fraud, over and over and over."
He did not say whether he had investments in cryptocurrencies.
Left built up his brand as one the most prominent short-sellers, but last year announced his company would stop publishing research highlighting companies' shortcomings and shift to writing about companies he thought might be worth buying.
The move followed a backlash against Left after he said the stock of video game retailer GameStop was not worth its price.
Reuters reported last December that the US Department of Justice had launched an expansive criminal investigation into short selling by hedge funds and research firms, including Citron, which has denied any wrongdoing.
"As the DOJ, you know, hopefully, one day development will realize that this boogeyman, or short sellers, doesn't exist," Left said when asked about the investigations.
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