Guitar Hero: Warriors of Rock made a "fairly dreadful" start at US retail, selling just 86,000 units in its five days of availability during September.
That's according to Cowen & Company analyst Doug Creutz, who also said that Metroid: Other M and Halo: Reach "came in well below our estimate".
Metroid debuted in ninth place on September's US software chart, while Halo: Reach topped the rankings.
Bungie's shooter sold 3.3 million copies in the States during its launch month. It's only the third game this console generation to surpass three million sales in its debut month, the others being Halo 3 and Modern Warfare 2, but Creutz had forecast 3.75 million sales.
We asked last month whether Guitar Hero: Warriors Of Rock could save the ailing music genre. On this early showing, it's not looking likely.