Amazon.com Inc said in July that it would buy One Medical for $3.49 billion, expanding the e-commerce giant's virtual healthcare and adding brick-and-mortar doctors' offices for the first time.

Amazon declined comment.

The FTC official said that the agency planned to send a pre-consummation warning letter, saying that it still had specific concerns about the deal. Antitrust agencies can, and sometimes do, file complaints to undo mergers that have closed.

The online retailer first piloted virtual care visits for its own staff in Seattle in 2019 before offering services to other employers under the Amazon Care brand. It likewise bought online pharmacy PillPack in 2018, underpinning a prescription delivery and price-comparison site it later launched.