Short-seller Andrew Left, who has successfully bet against stocks like Valeant Pharmaceuticals, tweeted a negative comment against one of the country's favorite stocks, Netflix.
Netflix shares dropped 3.4 percent following the tweet.
"There are competitors with deep pockets who are going to hire the same producers and create compelling content. Because of that, they do not have a moat like an Amazon. They do not have a moat like a Google," Left said on CNBC's "Halftime Report" Monday.
The company said in January it plans to spend $7.5 billion to $8 billion for content in 2018.
Netflix still has plenty of fans. One Wall Street analyst believes Netflix's original content scale is a big competitive advantage.
"We believe Netflix remains in a unique position of strength to grow its content and distribution tentacles over the next 12 to 18 months and thus further build out its massive content and streaming footprint," GBH Insights' Daniel Ives wrote in a note to clients Friday.
Ives reiterated his "highly attractive" rating for Netflix shares.
And the company's shares are crushing the market. Its stock is up 73 percent this year through Friday versus the S&P 500's 4 percent gain. Netflix is the best performer in the entire S&P 500 this year.
Netflix did not immediately respond to a request for comment.
Left confirmed he is short Netflix shares.
More than 50 companies Citron Research has targeted, including Amedisys and eUniverse, became the subjects of regulatory action, according to its website.
Citron's Left was one of the early skeptics on Valeant, calling into question its relationship with distributors in an October 2015 report. Valeant shares dropped more than 90 percent from their highs in 2015 as the company has struggled with lower-than-expected financial results, scrutiny of its drug pricing and investigations of possibly illegal business practices at specialty pharmaceutical distributors.