The makers of Willow glass, a flexible material expected to be used in theApple iWatch, said that their product is not ready for use in such a complex design.
Apple supplier Corning - developer of the glass, which can be made in a roll similar to newsprint - said the technology should be in use on simple products within a year, but not for anything as complicated as a wearable smartphone.
"People are not accustomed to glass you roll up," Corning boss James Clappin told Bloomberg.
"The ability of people to take is and use it to make a product is limited."
This would seem to go against leaks which previously suggested the iWatch was an advanced stage of development and not far off heading into production.
Last month, unnamed insiders were cited as saying that a team of 100 Apple staff - headed by senior executives - had been assembled to work on the product, implying that the iWatch was “beyond the experimentation phase”.
Apple’s senior director of engineering, James Foster, and another manager are part of the iWatch team, also according to Bloomberg.
Earlier last month, The New York Times, citing "people familiar with the company’s explorations", reported that the iWatch design would let the watch link wirelessly to the iPhone and allow wearers to easily access some of the features of the smartphone.
An Apple watch could be used to make mobile payments, for navigation, to access messages from the wearer's phone or to monitor health and activity, the newspaper speculated. It would run iOS, the same mobile operating system as the iPhone and iPad, the report said.
Separately, The Wall Street Journal reported that Foxconn, Apple's main manufacturing contractor, had discussed technologies that could address some of the technical challenges of such a device. In particular it had concentrated on making more efficient displays and chips, which could allow a smart watch to run for longer without recharging, the report said.
Speculation about the device has led to numerous mock-ups of how the iWatch might look.
The latest reports follow rumours that emerged from China late last year.
Local technology blogs claimed Apple was building “a device using Intel chips and new low-power Bluetooth technology”.
A 1.5-inch touchscreen or Apple's voice assistant Siri would be used to control the phone, the blogs said.
Apple and Foxconn declined to comment.
Apple already makes money from wearable computing thanks to third party accessories. Device's such as Nike's FuelBand and Jawbone Up are worn on the wrist and transmit data on daily activity to the iPhone via Bluetooth. Tim Cook has been spotted recently wearing a FuelBand.
Google has meanwhile already confirmed it plans to get into the wearable computing market. Google Glass, its augmented reality spectacles, are already in public testing.
