Billionaire hedge fund manager Bill Ackman appears to have a new short, according to a December performance report for Pershing Square Holdings posted on ValueWalk.

The unidentified short seems to have first appeared in a performance report from November, @ActivistShorts pointed out on Twitter. Meanwhile, the October performance report indicates that Pershing had 10 longs and only one short.

According to ValueWalk, the short bet appears to be on a company with a market cap over $5 billion.

Ackman, who runs Pershing Square Capital Management, had a monster year in 2014, netting 40.4% for the year, according to the performance report.

Ackman is known for typically being a long-only activist investor, taking large positions in a handful of companies and advocating for change.

However, Ackman's most famous position might be his short bet against Herbalife — a multilevel marketing company that sells weight loss shakes that he believes operates a "pyramid scheme" and will go to $0.

Ackman was widely criticized for being so public about his short position, with legendary hedge fund manager Leon Cooperman of Omega Advisors calling Ackman "foolish" for doing so.

After amassing millions in paper losses over the last two years on his Herbalife short, he's finally back in the money on that position as the company's stock has continued to decline.

Ackman last spoke about Herbalife in December on Bloomberg TV and sounded incredibly confident in his thesis, even revealing a damning internal video of one of the company's top distributors.

Right now, it's unclear if he'll disclose the short at all.

He's scheduled to be on CNBC's "Squawk Box" tomorrow at 7 am ET, and is also set to speak at the Harbor Investment Conference on February 12.

Here's the December report:





Here's the October report (note that only one short is mentioned):



