Advertising mogul Martin Sorrell said that despite problems at Elon Musk’s Twitter Inc., the real concern in online advertising is Facebook-owner Meta Platforms Inc.

“Meta is the issue,” WPP Plc founder and S4 Capital Plc chairman Sorrell told Bloomberg TV at the Web Summit conference in Lisbon, Portugal on Thursday, when asked about weakness in digital advertising. “Snap and Twitter, they’re not exactly rounding errors, but each of those two platforms is about 1% of global digital media.”

He said the four key digital advertising platforms are Alphabet Inc., Meta, Amazon.com Inc. and Bytedance Ltd.’s TikTok. Meta and Amazon shares have both tumbled in recent days after they missed earnings forecasts—but it’s “not a rout,” he said.

Following billionaire Musk’s controversial $44 billion take-private of Twitter, S4’s clients are adopting a “wait-and-see” approach to the platform, Sorrell said. Rivals such as agency holding company Interpublic Group Co. have advised pausing Twitter marketing, Variety reported earlier this week, citing an unnamed source.

Read more: Pause Twitter ads, Mediabrands advises

“It’s not clear yet from Elon Musk where he is” on moderation, Sorrell said. “The question is: how is that going to operate?”

“Clients don’t want conflict, they don’t want controversy,” he added. “They want a stable environment, and what we’ve seen in the last week or so is too much inconsistency.” 

Twitter has historically been inflexible with advertisers and contracts, Sorrell said—advising that it needed to “listen more” and set out a moderation policy. Last week Musk tweeted an open letter to marketers in which he said he wants to make Twitter “the most respected advertising platform in the world.”

A spokesperson for Meta declined to comment on Sorrell’s statements.

WPP CEO Mark Read separately said his company’s advice to clients “is to continue as normal for now.”

“Elon’s ideas around verification and innovation promise to create a better Twitter, which is positive for our clients,” Read said by phone. “Concerns around brand safety should be judged on what he does and how that impacts the platform.”

—Bloomberg News