Just 1.5m Surface tablets have been sold since the hardware's launch in October, according to reports.
Bloomberg claims to have word from insiders who reckon that sales of the entry-level Surface RT version stand at just over a million units while sales of the Surface Pro, which was released last month, have hit 400,000 units.
Microsoft is said to have ordered around 3m Surface RTs from suppliers and forecast 2m sales of the RT SKU in the December quarter.
By contrast, sales of Apple's iPad reached 22.9m in the December quarter. 2012's worldwide tablet shipments stood at 128.3m with Apple claiming just over half of the market.
The Surface is Microsoft's first ever own-built PC but is seemingly not currently on track to emulate the success Microsoft enjoyed with Xbox and Xbox 360.
It has also certainly not been helped by poor adoption of Windows 8, which has seen installation rates fall on desktop PCs. The Surface app store is still troubled by the lack of support from key partners, too. Facebook is yet to release a Surface app and Twitter only released its own Surface software this week.