Sales of the new Apple Watch have plunged by 90% since the opening week, according to a new market-research report.

Apple AAPL, +3.03% has been selling fewer than 20,000 watches a day in the U.S. since the initial surge in April, and on some days fewer than 10,000, according to data from Palo Alto, Calif.-based Slice Intelligence.

That is a sharp decline from the week of the April 10 launch, when Apple sold about 1.5 million watches, or an average of about 200,000 a day, Slice estimates.

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Furthermore, two-thirds of the watches sold so far have been the lower-profit “Sport” version, whose price starts at $349, according to Slice, rather than the costlier and more advanced models that start at $549.

In an ambitious bid for the luxury market, Apple unveiled a gold “Edition” model priced at $10,000 or more. So far, fewer than 2,000 of those have been sold in the U.S., Slice contends.

Slice bases its research on electronic receipts sent to millions of email addresses following purchases. The company conducts market research on behalf of consumer-goods companies, among others, many of them in the Fortune 500.

Wall Street has been desperately trying to work out how well the new watch has been selling, but Apple has been refusing to say. The company, which in the past has updated Wall Street on the sales of new products soon after the launch, has yet to release any numbers about the watch.

Apple did not immediately respond to a request for comment.

How worrying are these numbers for Apple investors, fans and customers? It’s a mixed picture.

On one hand, you’d expect sales of any new product to tumble after the initial bump (and the first week’s numbers are heavily weighted toward the opening day). The watch is only a tiny part of Apple’s business. Trefis, a stock-research company, ascribes just 4% of Apple’s current value to its watch business.

But this fall-off in sales, if confirmed, nonetheless looks ominous. And the Apple Watch is much more important than any immediate contribution to earnings would suggest.

The Apple Watch is the first completely new product the company has created and launched since the death of its visionary founder, Steve Jobs, in 2011. How well the watch fares may be one measure of how well Apple may be able to maintain the standards of excellence in innovation, marketing and production it achieved under Jobs. Investors are used to seeing new products, such as the iPhone and iPad, fly off the shelves as soon as they are launched.

The Apple Watch is also a foray into the world of so-called “wearable tech,” which is supposed to offer yet another big surge in product sales for Apple and its rivals in the years ahead. Once everyone has a smartphone, they are supposed to go out and get a smart watch, followed by smart eyeglasses, and so on. Or, at least, so goes the theory.

Apple’s Watch has entered a competitive market for wearable tech, against rivals such as health-monitoring wristband Fitbit FIT, -0.94% .

It’s early days yet on the Apple Watch, but investors may have reason to be cautious.