The U.S. Federal Trade Commission is also opposed, but it suffered a major defeat on Tuesday when a federal court ruled in favour of Microsoft.
It is battling on and filed an emergency motion to an appeals court requesting a "temporary pause" to the deal closing late on Thursday.
Yet on Tuesday, less than an hour after a U.S. federal court ruled the deal could go ahead, the CMA said it could look again at a modified proposal.
A Bloomberg report said Microsoft and Activision were considering giving up some control of their cloud-gaming business in Britain to appease the CMA.
Additional reporting by Muvija M; editing by Jason Neely and Louise HeavensOur Standards: The Thomson Reuters Trust Principles.
Persons:
Brad Smith, Jeremy Hunt, Smith, Gareth Mills, Charles Russell Speechlys, They'll, Muvija, Jason Neely, Louise Heavens
Organizations:
CMA, Microsoft, Activision, Markets Authority, U.S . Federal Trade Commission, Bloomberg, Thomson
Locations:
Britain, EU