A sale of Netflix stock by Carl Icahn could send the shares 5 to 7 percent lower, RBC Capital Markets Internet analyst Mark Mahaney said Monday on CNBC's "Fast Money."

"He's been an extremely good buyer of the stock," Mahaney said. "If he were to sell, I wouldn't change our opinion, but we'd note it as a clear negative on the stock. He knows what he's doing with Netflix so far."

Icahn, the billionaire activist investor and chairman of Icahn Enterprises, holds 10 percent of Netflix's outstanding shares

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Were Icahn were to sell his shares, Netflix stock would head downward, Mahaney said.

"I think this stock would probably correct 5 to 7 percent on the day," he said. "That would be the trade is my guess, depending if it was right around these levels."

There has been no immediate response from Icahn.

Meanwhile, Mahaney said that a partnership between Netflix and any cable provider would be a boost for the company.

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"Getting embedded in large cable providers like Comcast is probably one of the biggest stock catalysts you can come up with," he said.

Such a deal would likely increase Netflix subscriptions as well as reduce churn and marketing costs, Mahaney added. "It depends what the economics are, but it's hard to see this not as a potentially big win for Netflix."

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"I think for Netflix, any fit's a win," he said. "Look, if one or two major cable companies brings Netflix on to their boxes, chances are very high that other cable companies will be required to do that."

—By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.

Disclosure: Comcast is the owner of NBCUniversal, the parent company of CNBC and CNBC.com.