Greenlight Capital head David Einhorn is tweaking his bets after losing money in a "frustrating" third quarter.
Greenlight closed out short positions in Keurig Green Mountain, Lululemon, Joy Global and Under Amour, according to a new investor letter obtained by CNBC. New long investments include Consol Energy and EMC.
"It was a frustrating quarter," the letter said. "Nothing particularly bad happened; we just got ground down gradually. In such circumstances, it's not obvious what to do other than stay the course and be patient."
"One of the principal bullish assumptions supporting many bubble stocks is, 'the company is growing too fast to be very profitable,'" the letter said. "We think AMZN is just one of the many stocks for which this narrative will ultimately prove false."
A spokesman for Greenlight declined to comment.
The hedge fund is up 2.2 percent for the year through September after losing 3.9 percent net of fees in the third quarter, according to the letter.
--CNBC's Kate Kelly contributed reporting.