Meta Platforms stock has been on a tear lately thanks to the launch of personal assistant Muse-but the move into AI may end up costing the Facebook parent more than it's worth.

That's according to StoneX analyst Mark Zgutowicz, who wrote in a research note on Wednesday that he expects Muse to fuel rather than ease existing worries about Meta's massive spending plans.

Zgutowicz's rating on the stock is Hold.

"We...see Muse's materially higher infrastructure-intensity adding to, not relieving pressure from, Meta's existing ROIC debate," he said. ROIC refers to return on invested capital.

Shares slid 1% to $731.04 ahead of the market open. It is up 29% over the past month, rallying on Muse's surge to the top of the App Store charts.

Meta expects to double its capital expenditures to about $140 billion this year as it bids to keep up with Big Tech rivals in the AI race. Some investors, though, worry whether the spending spree will deliver enough return.

Muse has been a success story for the Instagram owner, but its competition is already heating up. On Tuesday, ChatGPT developer OpenAI announced it would launch AI agents called "Dots."

Unlike Muse, Dots is a paid service for now. Still, it could clearly become a rival to Meta's red-hot personal assistant. Meta expanded Muse to small businesses on Tuesday after the OpenAI launch.

"We expect OpenAI to eventually introduce a usage-limited free Dot tier to broaden consumer adoption and create an upgrade path to paid," StoneX's Zgutowicz said.