Citron's Andrew Left, who gained notoriety for successful bets against companies like Valeant Pharmaceuticals, said he is short shares of Facebook.

"Facebook is losing an extensive amount of relevancy," Left said in a phone interview Monday morning. "I am short Facebook."

Left's bet comes the morning Microsoft said it was buying LinkedIn for $26.2 billion in cash. He is no stranger to investing around the social network space as he told CNBC back in February that he was long LinkedIn. The investor confirmed he still holds the stock.



LinkedIn "was a monopoly in their respective space, whereas I see Facebook losing share to Snapchat and overstaying its welcome in other niches," Left said. "I am not saying Facebook is a bad company (it) just will not be a $330 billion company in a year."

Facebook did not immediately return CNBC's request for comment.

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