Guitar Hero: Warriors of Rock has sold just 86,000 copies in its first week in the US, across all formats.
The figures, which were obtained by CVG from analyst Cowen & Company, represent a serious decline for the series.
Guitar Hero 5 managed 499,000 sales in its first month in 2009, Guitar Hero: World Tour topped 500,000 in its first week in 2008 and Guitar Hero III managed 1.4 million units in five days the year before.
Guitar Hero: Warriors of Rock entered the UK all-formats chart at six when it launched last month. Eurogamer's Johnny Minkley awarded the game a solid 7/10.
Earlier this year, Rock Band developer Harmonix talked down fears that the music genre was in terminal decline. CEO Alex Rigopulos claimed, "I absolutely do not believe that rhythm-action gaming has reached its peak."
Let's see if Rock Band 3 fares any better when it launches for DS, PlayStation 3, Wii and Xbox 360 on 29th October.
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