Ackman posting a loss after market drubbing

The recent brutal stretch for U.S. stocks has punished hedge fund heavyweight Bill Ackman, according to a letter obtained by CNBC.

Ackman told investors Wednesday that his fund, Pershing Square Capital Management, is posting a loss for the year after gaining 10 percent through July. The fund cited "significant volatility" in markets, driven by uncertainty about how Chinese economic growth will affect businesses.

"At the date of this report, the year to date investment performance has been erased, and the company is at a loss position for the year," Pershing Square wrote.

Bill Ackman at Delivering Alpha 2015 in New York.
David A. Grogan | CNBC
Bill Ackman at Delivering Alpha 2015 in New York.

Major U.S. averages have shed roughly 8 percent each this month. The Nasdaq has suffered the most, losing 8.6 percent.

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Some of Ackman's holding have fared poorly in that stretch. Mondelez International has fallen nearly 9 percent since Ackman took a $5.5 billion stake in the company earlier this month.

Valeant Pharmaceuticals has dropped 11 percent this month, while Canadian Pacific Railway has lost nearly 14 percent.