Several Apple resellers are out of stock of the Thunderbolt Display, which could hint at an upcoming upgrade for the 27in monitor, perhaps to bring it closer to the design of the new, thinner iMacs.

Apple Insider reports that, this week, major resellers including Amazon have run out of stock of the Thunderbolt Display, traditionally a sign that Apple is planning an upgrade.

The Thunderbolt Display hasn't had a major update since it launched in 2011, with the only change being the addition of a MagSafe to MagSafe 2 Converter that now ships with every model in order to make it compatible with new MacBooks.

So Apple's update could bring a built-in MagSafe 2 cable to the Thunderbolt Display to remove the need to add a converter, and it could add USB 3.0 connectivity, as well as introduce the new, thinner design of the iMac to the monitor.

iFixit chief information architect Miroslav Djuric told Apple Insider that the current Thunderbolt Display should be thought of as "an iMac minus the computing hardware," noting that that trend is likely to continue with the next-generation model of the monitor.

Djuric said that, along with the thinner design, the next Thunderbolt Display is likely to implement the new iMac's re-engineered display that uses a full lamination process to make the images look closer to the viewer. SEE: Apple iMac review

Full lamination also reduces glare by 75 per cent, according to Apple, a feature that would benefit the Thunderbolt Display.

Apple appears to be having some manufacturing difficulties with the new display, however, with the lamination process being blamed for the month-long shipping delays that the 27in iMac is currently experiencing.

Apple's Thunderbolt Display currently available from Apple for £899.