The Nintendo Wii sold 236,000 units in May, according to a report released by Wedbush Securities - a 20 per cent decline year-on-year.
The report arrives in the wake of NPD figures confirming that the Xbox 360 has maintained its supremacy in the US market after selling 270,000 consoles.
The PlayStation 3 enjoyed a 14 per cent year-on-year increase, but is still lagging behind its rivals with unit sales of 175,000.
The 3DS also had a difficult month, with hardware sales falling by 50 per cent from its second month total, and "well below" Wedbush Securities' 180,000 unit estimate.
Software sales for the handheld reflected the current downward trend for physical retail with a tie ratio of just 2:1, which the report called "disappointing" and, "surely an all-time low for a new hardware launch."