Bloomberg claims that Microsoft has received a statement of objections from the EC earlier in the week, according to unnamed sources familiar with the matter. This list of concerns is part of an ongoing investigation, the results of which are due on April 11.
Simply stated, this statement outlines "potential reasons" to block the Activision Blizzard takeover unless certain concessions are made. The way the story is phrased though, it does suggest that the EU is open to negotiation and Vole has already said that it is ready to offer concessions to the EU.
Details are unclear what the objections include, but the EC is generally worried that the deal could reduce competition in the market and give Microsoft a stronghold in the mobile and cloud gaming sector.
Microsoft has been trying to assure regulators that it does not plan to restrict competition or reduce access to games. It has already promised to bring Call of Duty to the Nintendo Switch and offered to keep the franchise on PlayStation for at least the next 10 years.