Einhorn: I'm adding to 'bubble basket' shorts like Amazon

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."

Greenlight also added to its previously disclosed "bubble basket" of technology company shorts. Einhorn used Amazon.com as an example of one such overvalued stock.

"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."

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A spokesman for Greenlight declined to comment.

Losing positions, according to the letter, included shorts on U.S. Steel and Mallinckrodt and a long position on Civeo.

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.

The largest disclosed long positions at the end of the quarter were Alpha Bank, Apple, gold, Micron Technology, Resona Holdings and SunEdison.

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--CNBC's Kate Kelly contributed reporting.