Dara Khosrowshahi, chief executive officer of Uber Inc., center, rings the opening bell during the company's initial public offering (IPO) on the floor of the New York Stock Exchange (NYSE) in New York, U.S., on Friday, May 10, 2019.

For Uber shareholders, Wednesday is a landmark day, presenting the first opportunity for most of them to sell stock since the company's IPO six months ago.

Wedbush analysts warned in a report on Nov. 1 that the lock-up expiration could "cause an avalanche of selling as early investors and insiders hit the bid," making Uber's "horror show" of a debut even worse.

But those nervous about a flood of shares hitting the market from investors who want to lock in gains can take some comfort in this: A bunch of that stock is underwater and even deeper in the red after Tuesday's 9% plunge to $28.38.

Of the roughly 1.7 billion Uber shares outstanding, about 1 billion have been locked up since the IPO in May. Wednesday is expiration day and, according to analysts at MKM Partners, about 90% of Uber's stock will be available for sale, with some insiders still restricted from unloading portions of their stake.

According to the company's IPO prospectus, about 545 million shares (32% of the current outstanding supply) were purchased at $32.97 or higher. Uber, remember, was the unicorn-era posterchild, raising a ton of late-stage capital between 2014 and 2018, after it had become a dominant ride-hailing platform and a household name even though it was burning billions of dollars of cash.

Most of those investments looked smart when Uber priced its IPO at $45 in May. But the shares have since lost 37% of their value, suffering their latest blow after Uber reported a quarterly net loss on Monday afternoon of over $1 billion. Private market investors are feeling the pain as Uber tries to convince Wall Street that a sustainable business is on the horizon — CEO Dara Khosrowshahi said Uber is targeting "total company EBITDA profitability for the full year 2021."