Despite the lack of a concrete release date, the action role-playing game was originally expected to launch later this year.
"With every game we make, the temptation is always very strong to launch as soon as possible. However, we didn't put so many years of work into Diablo III to release a game that was almost ready," revealed Blizzard co-founder Mike Morhaime.
A closed beta was launched earlier this week, which was available to invited Battle.net account holders and users with special promotional keys.
Blizzard revealed that it would use the additional time to extend the beta testing phase and potentially invite more gamers to join in.
"The beta test is going very well, and we look forward to making the most of the extra time we're taking to deliver an experience that lives up to our vision for the game and the expectations of our players," Morhaime added.
Diablo III will feature a new Inferno difficulty mode and will potentially be released on home consoles.