Volume sales of Modern Warfare 3 are currently 4.2% below its predecessor, selling less than half the amount of Black Ops during the month of March, reports VG247.
The decline in sales represents new shopping habits for gamers, according to Webush Securities analyst Michael Pachter, who claims that users are less likely to purchase games post-launch.
The dip also shows that more people are using their consoles as entertainment devices, instead of as gaming devices, according to analysts at Piper Jaffray.
The news comes the week after it was revealed that the collapse of GAME had taken its toll on video game sales.
Physical sales suffered a 30% hit during the entire first quarter of 2012, a number likely to have been impacted by GAME Group's inability to stock key titles.
Modern Warfare 3 maps Sanctuary and Foundation were released on Xbox Live last week.
Sanctuary takes place in a Grecian monastery, while Foundation is based in an abandoned South Korean factory.
Modern Warfare 3 will see a total of 20 updates over a period of nine months.
Call of Duty: Modern Warfare 3 was released in November and has broken Avatar's record as the fastest-selling piece of entertainment. However, it failed to topple Adele as the UK's best-selling entertainment property in 2011.
Call of Duty: Black Ops, meanwhile, was voted the best video game ending of all time in a poll carried out by the Guinness World Records 2012: Gamer's Edition.
The next game in the series is expected to be a follow-up to Black Ops. Details of the title, including its release date and multiplayer information, were reportedly leaked online.
> Read our review of Call of Duty: Modern Warfare 3
> Read our review of Call of Duty: Black Ops
Gallery - view Modern Warfare 3 screens below: