That's according to Politico, citing people familiar with the matter.

Though the report said a lawsuit challenging the deal is not guaranteed.

It added that the FTC's four commissioners have yet to meet with lawyers for the companies.

The FTC did not immediately respond to requests for comment from Reuters.

Microsoft, maker of Xbox console, in January announced a plan to buy Activision, maker of "Call of Duty".

It would be the biggest takeover in the history of the gaming industry.

Microsoft is betting on the acquisition to help it compete better with videogame leaders Tencent and Sony.

The deal is also facing scrutiny outside the US; the EU opened a full-scale investigation earlier this month and Britain's antitrust watchdog announced in September it would do the same.

Critics say the takeover could harm competition in the industry by restricting access to major games like 'Call of Duty'.