Uber is currently valued at $62.5B—that’s higher than 80% of the companies on the S&P 500.

But an NYU professor in the Stern School of Business says Uber is about to hit a major roadblock that has taken out many startups of its kind.

Aswath Damodaran, who specializes in equity valuation, says Uber is having a difficult time turning revenue into profits. Though Aswath says the concept of ride sharing is here to stay and will continue to grow, the constant promotions and large discounts are hurting profits, Bloomberg reports.

“In effect, it looks like the business model that has brought these companies so far as they have in such a short time period is flawed, because what allowed these companies to grow incredibly fast is getting in the way of converting revenues to profits,” Aswath tells Bloomberg. He says Uber’s true value is $28B. That's less than half of its current valuation, which ranks it close behind giants McDonald’s Corp and Walt Disney Co. [Bloomberg]