The social network, which will provide extensive stat tracking, head maps and clan support for Modern Warfare 3, has seen limited functionality due to the number of players trying to use the service.
"Registration requests for our new live service Call of Duty Elite are exceeding even our most optimistic expectations, which is creating a bottleneck and some players have not been able to register," said Beachhead Studio boss Chacko Sonny.
"We have already registered hundreds of thousands of players and we are working around the clock to increase our capacity as quickly as possible."
Watch the Compete video for Call of Duty: Elite below:
It was stressed that all game data and stats will be safe until the service becomes fully operational.
The latest update on the game's Twitter account said that capacity will increase by four times today, with the intention of bringing stat access online soon.
It was added that launch details of the iOS and Android applications will be available later today.
Last week, it was revealed that PC users will not receive Call of Duty Elite until after Modern Warfare 3's launch.
Modern Warfare 3 is available now on Xbox 360, PlayStation 3 and PC.
> Read our review of Modern Warfare 3
Watch the Improve video for Call of Duty: Elite below: