Sony, for reasons understandable, was the biggest opposition to the Microsoft and Activision Blizzard deal citing concerns such as the exclusivity of the Call of Duty franchise.
However, we now also know that the company was deeply concerned that its rival could "leapfrog" the PlayStation in the console segment.
In newly leaked documents, Sony privately described the landmark merger between Microsoft and Activision as a "massive threat to PlayStation Plus." The company also said, repeatedly in public too, that Microsoft use the Call of Duty series to "disrupt and threaten console gaming and game subscription markets."
The concerns by Sony were detailed in documents that were leaked as part of the recent hacking incident at Insomniac Games. Some of the documents, including presentation slides where Sony identified threats presented by Microsoft's Activision Blizzard takeover, have been released publicly online.