The M74 extension opened less than a year ago but workers have been ordered to carry out repairs this week to a section of the fast lane which has partially collapsed.
Transport Scotland has launched a full scale investigation after highway patrols discovered a dip in the road along a 20-foot stretch of the westbound carriageway taking motorists to the centre of Glasgow.
The fault is located on the fast lane shortly before the Polmadie slip road at Junction 1A.
Overhead gantry signs warn drivers of an "uneven road surface" before they are told to almost halve their speed.
But motorists are not told to vacate the outside lane, which is blighted by the warped road surface.
Despite highway officials taking safety precautions, the national agency responsible for the country's roads last night denied the new motorway – built at a cost of £445million – was sinking.
Instead, officials insisted the "dip" was "normal" and claimed the results of routine monitoring indicated there would be no more "settlement" issues on other parts of the motorway once repairs were carried out in a few days.
A spokeswoman for Transport Scotland commented: "Some settlement is to be expected in the first year and is entirely normal for a new road. We know about it and we put up precautionary signing to ensure drivers are aware of the slight dip in the surface."
The extension was built by a consortium involving some of the UK's biggest construction and civil engineering companies formed by Morrison Construction, Balfour Beatty and Sir Robert McAlpine as well as one of Britain's leading infrastructure specialists Morgan Est.
It has been instructed by Transport Scotland not to discuss the fault with the Evening Times.
A consortium spokeswoman, admitted: "All media inquiries in relation to this are being handled by Transport Scotland."
Transport Scotland confirmed public statements would only be made by the agency and pointed to the fact that it handled most of the publicity during the three years it took to build the extension.
Although the national agency played down the fault, officials did admit the contractor had also carried out an investigation and that a written report was expected to be lodged with Transport Scotland
The repair will be carried out on Thursday during the night to minimise disruption.
The spokeswoman added: "The cost of the repair work is the responsibility of the contractor under their five year warranty agreement."
Around 30,000 vehicles use this stretch of motorway each weekday which has helped ease traffic congestion through Glasgow on the busy M8.
Andrew Howard, head of road safety at the AA motoring organisation, said: "Drivers will see the new M74 as a wonderful flagship programme which has revolutionised their journeys.
"But they will be dismayed to see that such an expensive project can have what looks like structural problems so soon after opening."
The extension joins the original end of the M74 at the Fullarton Road junction with the M8 on the south side of the city.
Although just five miles long, the cost of building it was a whopping £445m, although the total bill was £692m after the cost of buying up land was added.
It is Scotland's most expensive road at £138.4m per mile.