A proposed $69 billion acquisition of games publisher Activision Blizzard by Microsoft was tipped to face in-depth probes by the European Union (EU) and the UK’s antitrust regulator over growing concerns the deal could prove anti-competitive.

Financial Times (FT) reported the UK’s Competition and Markets Authority (CMA) is set to launch a phase two investigation into the deal.

The CMA was one of the first to launch a major probe into the deal, which would be Microsoft’s largest purchase ever and also the biggest all-cash technology acquisition on record.

Earlier this month, the CMA issued a notice giving Microsoft five days to satisfy competition concerns or risk a deeper probe.

Microsoft opted not to offer any remedies at this stage.

FT reported the companies have been in discussions with EU officials since the deal was announced. Those involved are apparently anticipating a prolonged probe once Microsoft officially files the case with the EU in the next few weeks.

Given the size of the deal and the nature of the buyer, in addition to growing concerns from rivals, it will likely take a long time to be fully assessed by the EU, FT reported.

Activision Blizzard is the publisher of hit titles including Call of Duty, Quake, Guitar Hero and Doom.

Gaming giant Sony had expressed concerns about future access to Activision Blizzard titles if Microsoft completes the acquisition.

The Japanese company accused Microsoft of misleading the game industry and regulators over its commitment to keep Call of Duty on PlayStation after any purchase.

Microsoft’s deal is also facing investigations in New Zealand and the US.