French website MacBidouille says the major delay is due to difficulties with a high-tech welding process, called friction-stir welding, that fuses the two major pieces of the iMac's aluminum body together.
Touted at Apple's iMac unveiling last month as one of the main reasons for the computer's thinness and improved strength over previous versions, the advanced assembly technique uses high heat and pressure to "intermix the molecules of the two aluminum surfaces" to create a seamless joint.
The high difficulty of manufacture is compounded by the iMac's screen lamination process, which eliminates a 2mm air gap between the display and front glass found in older iMacs.
Currently, availability of the desktop remains unchanged on the Online Apple Store, which shows November and December launch windows for the 21.5-inch and 27-inch iMacs, respectively.
A person familiar with the situation said it's likely the 21.5-inch model won't ship out until next month, but both it and the 27-inch model are still scheduled for release before the end of the year, CNET reported.
Apple declined to comment on the reports, CNET said.