"Yes. They are great companies. But the ETFs probably have accentuated the flow of capital into those stocks," he said at the conference. "Nothing works forever. Things that are most hyped and usually the things that are most loved produce the most disappointment and the most pain."
Three out of the four FANG stocks have declined since the investor's cautious remarks.
On Thursday Facebook shares dropped 19 percent, a day after it reported lower-than-expected second-quarter sales and daily active user numbers, resulting in the biggest one-day market value loss for a single U.S. stock in history.
And since the market's close on July 17 through Monday, Facebook shares fell 18.5 percent, Amazon dropped 3.5 percent, Netflix declined 11.7 percent, while Alphabet's stock rose 1.4 percent.
Marks is known for his prescient investment memos, which warned about the financial crisis and the dot-com bubble implosion. Oaktree Capital had $122 billion of assets under management as of June. The investor has a net worth of $2 billion, according to Forbes.
The full interview with Marks is