US sales of the latest Call of Duty instalment are down around 14 percent in its first month on Xbox 360 and PS3, according to NPD data.
Activision recently published data showing that Black Ops 2 grossed $1 billion worldwide in fifteen days since going on sale. The figure was based on internal sell-though estimates, retail data and official Chart-Track information.
Last year's Call of Duty instalment, Modern Warfare 3, sold a record-setting 8.8 million units in its first month in the US - 10 percent more than the previous year's Black Ops.
Earlier this month trade analysis suggested that Black Ops 2 could be down by as much as 20 per cent on day-one sales compared to its predecessor.
This led to some commentators asking whether the franchise's appeal has plateaued or, perhaps, declined. However, Black Ops 2 remains on course to be the highest grossing packaged game of 2012 by some margin.