The market darling FAANG stocks could be in for trouble as short sellers step up bets, S3 Partners director Brett Weiss wrote in a note Thursday, Sept. 28.

FAANG, a term coined by TheStreet's Jim Cramer, refers to the popular high-growth stocks Facebook Inc. (FB) - Get Report , Amazon.com Inc. (AMZN) - Get Report , Apple Inc. (AAPL) - Get Report , Netflix Inc. (NFLX) - Get Report and Alphabet Inc. (GOOGL) - Get Report .

Over the past six weeks, bearish bets against the FAANG stocks have increased by $1.93 billion, or 7.6%. Estimated total current risk rose to $27.3 billion during that period, S3 said. Since mid-August, investors have lost $22.5 million in aggregate, or 0.08%.

"And the shorts are really hitting the FAN," Weiss added, as Facebook, Amazon and Netflix have gained the most short interest with $494 million for Facebook, $502 million for Amazon and $910 million for Netflix.

The in-favor FAANG firms could see higher demand to add to shorts as the market reaches record highs almost daily. FAANG stocks trade at general collateral levels, meaning they're the cheapest and easiest to borrow.

"With the S&P 500 Index just off its all-time high of 2,508.24 and bearish investors adding to an already elevated level of short interest, the outlook for the FAANG stocks is troubling," Weiss said.

Apple and Netflix stock traded down early Thursday afternoon, while Facebook, Amazon and Alphabet shares were up.

Facebook, Apple and Alphabet are holdings in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells FB, AAPL or GOOGL? Learn more now.

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