After going "naked" for IPO, Uber faces real short sellers

Uber's underwriters, led by Morgan Stanley, were so worried about the company's IPO that they deployed "a nuclear option" ahead of the deal last week to provide extra support for the stock — a so-called naked short, as CNBC's Leslie Picker reported Tuesday.

The catch: Now, actual short sellers are coming in at significant levels and could push the stock even further below its $45 IPO price.

What it means: Every IPO includes an excess amount of shares that allow underwriters to sell 115% of the available offering and then buy the additional 15% back, Picker explains. That extra 15% can support the stock's price if it falters.

• But in Uber's case, they opened a naked short, allowing underwriters to sell more than the "greenshoe" portion and then buy the shares back, providing "even more firepower."

The bottom line: That plan came up short as Uber's stock fell 18% in its first days as a public company before recovering Tuesday with a 7.7% gain.

What to watch: Actual short bets against Uber now total $768 million, with short sellers holding 11.5% of available shares, according to data from Ihor Dusaniwsky, managing director of predictive analytics at S3 Partners.

• "We expect Uber short interest to increase over the next several days as short sellers continue to be active," Dusaniwsky said in a statement.

Go deeper: Uber's massive IPO sinks investors