The much-anticipated Uber Technologies Inc. (UBER) IPO is being regarded as a Wall Street flop and some skeptics are seeing an opportunity. Short sellers are betting against the ride-hailing company with 20.71 million shares, or 11.51% of its float, according to figures published Tuesday by S3 Partners.

The financial technology and analytics firm said short interest in the company reached $768 million on its third day of trading and is expected to keep rising over the next several days.

Stock borrow rates are at around 3% to 5% but will increase with short interest to reach double digits.

"As with most IPO’s, the cost to borrow climbs steadily over the first week to two weeks until shares settle, and lending inventory replenishes. LYFT stock borrow rates hit over 100% fee early on and with two weeks fell to below 5% fee," said managing director of predictive analytics, Ihor Dusaniwsky. "At the moment there is stock to go and brokers are able to approve short sales in size – long shareholder sellers will now be ride sharing with short sellers if UBER’s stock price trends downward again."

Uber shares closed 7.71% higher at $39.96 on Wednesday, but this is still much below its IPO price of $45. While it's clear the company has suffered due to bad timing with trade tensions running high, widespread concerns about the ride-hailing business model and its profitability are largely to blame for the stock's performance.

For comparison, short interest in Uber's smaller rival Lyft Inc. (LYFT) was $1.07 billion as of May 10, according to S3. This represents 19.47 million shares and 59.96% of its float. Borrow rate was at 8.38% and rising with new shorts at 25% to 35%. Lyft shorts have made $325 million in mark-to-market profits since its debut in March.