Reuters sources say the $69 billion deal is likely to attract a warning from EU competition watchdogs.
The European Commission is said to be readying a charge sheet known as a 'statement of objections'.
That's a list of concerns which will be sent to Microsoft.
The software giant announced the acquisition of the 'Call of Duty' maker in January last year.
It hopes the deal will help it compete with rivals Tencent and Sony.
But the takeover has already faced objections from watchdogs in the U.S. and UK.
The U.S. Fair Trade Commission is going to court to block it.
Microsoft was expected to offer remedies to EU regulators to head off trouble there.
However, the Reuters sources say Brussels won't consider remedies before first setting out its concerns.
Microsoft last month reached a 10-year deal with Nintendo to make Call of Duty available on its consoles.
It says it's open to a similar deal with Sony, which has been strongly critical of the takeover.
