The Breakdown DLC has been delivered to Microsoft for pre-certification testing, meaning the expansion is content- and feature-complete. What's left now is for Undead Labs to polish the game and remove bugs.

Undead Labs said it plans to have this process wrapped up and have the Breakdown DLC ready for formal certification testing at the end of next week, but made clear that this could change.

"Our test team could turn up some huge game-screwing design flaw next week," the developer said. "We might make a mistake in the packaging format and fail certification. The government shutdown could close down the internetz. Anything could happen."

"But, assuming no catastrophes, we plan on getting Breakdown into your hands by the end of October."

State of Decay's Breakdown DLC is designed introduce a new level of difficulty to the game. Damage received from zombie attacks will be increased, while players will also need to manage their stamina more carefully, the developer said.

In addition, the population of fast-moving zombies in State of Decay will be increased in the Breakdown DLC and players will also encounter more special "freak" zombies. Finally, resources will be scarcer, while the number of vehicles players have access will decrease.

"I've made it my goal to create a version of the game that gets so hard by the end, I can barely play it, and then let you folks show me how it's done. Are you ready?," Undead Labs designer Geoffrey Card.

State of Decay launched in June 2013 and has sold --across Xbox 360 and PC--to date.