A slight bump in subscription numbers for World of Warcraft after the launch of the Mists of Pandaria expansion has disappeared. Subscription numbers for the MMO now stand at 8.3 million, down from 9.6 million at the end of Q4 last last year, Activision announced in its latest earning report for Q1 2013.

Activision Blizzard CEO Bobby Kotick said during the earning conference call that the company is "concerned" by the drop. "While we have had a solid start to the year, we now believe that the risks and uncertainties in the back half of 2013 are more challenging than our earlier view, especially in the holiday quarter," he told investors in a prepared statement. "The shift in release dates of competing products, the disappointing launch of the Wii U, uncertainties regarding next-generation hardware, and subscriber declines in our World of Warcraft business all raise concerns, as do continued challenges in the global economy."

Regarding World of Warcraft, Kotick believes they can slow down subscriber churn by "releasing new content more frequently," although he admits that numbers will still be down by the end of the year, citing additional competition from free-to-play games. Additionally, "we want to make it easier for lapsed players to get back into the game."

Blizzard CEO Mike Morhaime agreed, saying the part of the drop has been an increase in competition in China from more free-to-play games, and a decrease in the number of casual players. He also said that when casual players return, the company needs to make it easier for them to do so.

"It is important to use the transition from when players leave and then come back to make the experience less overwhelming," he said. Blizzard plans to continue looking at player behavior and preferences when creating and releasing content updates, one of which is coming later this month. "People consume content quickly. We need to create more innovative content to keep people engaged."