(Bloomberg) — Hedge fund manager Bill Ackman sent shares of Herbalife tumbling on Friday after telling CNBC that top investor Carl Icahn is trying to sell his stake in the nutrition company.

Ackman told the news station that investment bank Jefferies Group approached him about buying a portion of Icahn's Herbalife shares. Ackman and his hedge fund, Pershing Square Capital Management, have been betting against Herbalife since late 2012, saying that the company is an illegal pyramid scheme that should be shut down. Herbalife has denied those accusations.

Ackman maintained his bet against Herbalife even after the company reached a $200 million settlement with the U.S. Federal Trade Commission last month. He said that the terms of the agreement — which Herbalife hailed as an acknowledgement that its business model was sound — would cripple the company and cause it to collapse.

"If Carl sells, I think it can accelerate the demise of the company," Ackman told CNBC. "With Carl there, they may have a better chance of keeping top distributors. With Carl exiting, I think it's over and it's over quickly."

Herbalife declined to respond to Ackman's comments on Friday.

SHARES SLUMP

The shares tumbled as much as 7.6% to $57.20 before the start of regular trading in New York. Herbalife had gained about 15% this year through Thursday.

Herbalife earlier this month posted second-quarter results that topped analysts' estimates and said it expects to overhaul its business practices globally in response to the settlement. While the terms of the deal only affect its U.S. operations, the company said it would likely roll out some aspects of the agreement worldwide.

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