Microsoft's plan to buy video game company Activision Blizzard faced a potential setback Thursday after British antitrust regulators demanded concessions from both companies to ease competition concerns about the blockbuster deal. The Competition and Markets Authority said it was worried the $69 billion deal would hurt rivals by restricting their access to Activision Blizzard games. It also worried that the combined company would stifle competition in the emerging cloud gaming market. The authority gave both companies five days to come up with proposals to address its concerns, otherwise it would escalate its investigation with more scrutiny. The all-cash deal is set to be the largest in the history of the tech industry.