Last fiscal year, Zynga comprised 9% of Facebook's total revenue. The social network noted that Zynga's contribution to its payments business continues to fall, and Zynga Inc (NASDAQ: ZNGA ) wan't mentioned in the most recent 10-Q as a 10% customer. As part of Zynga Inc (NASDAQ: ZNGA )'s turnaround efforts — before yesterday's announcement that Don Mattrick would be leaving Microsoft Corporation (NASDAQ: MSFT ) to become Zynga CEO — Zynga Inc (NASDAQ: ZNGA ) had begun to explore game publishing as a way to diversify away from casual gaming toward the "mid-core" segment. The company tapped developer Phosphor Games to release Horn last year, which earned strong reviews and climbed the charts. TechCrunch is reporting that Facebook Inc (NASDAQ: FB ) may be looking to also enter the game publishing business now.