David Einhorn is short Caterpillar

Billionaire hedge fund manager David Einhorn is short Caterpillar. Shares of the company tumbled in after-hours trading after he disclosed the position Wednesday.

The Greenlight Capital president revealed his firm's position at the Ira Sohn conference.

"We don't think CAT has yet hit a bottom - we think CAT bottoms in 2018," Einhorn said.

He said he expects Caterpillar's shares to be cut in half by that point. Following Einhorn's comments, the shares fell 1.7% to about $73 after the close of regular trading.

Einhorn had already indicated that he was short a heavy-equipment maker, telling investors on a February conference call that "bulls are assuming the current commodity environment is an ordinary cyclical downturn," according to Bloomberg.

"We believe it is the end of a commodity supercycle, and this will exert a long period of earnings headwinds for these companies," Bloomberg reported then, noting that he didn't specify which company he was shorting at the time.

Caterpillar's shares have gained about 11% since the February 23 disclosure.