STORY: Amazon on Thursday agreed to buy One Medical for $3.9 billion, including debt, expanding the e-commerce giant's virtual healthcare and adding brick-and-mortar doctors' offices for the first time.

"Their acquisition of a healthcare provider to that magnitude only underscores the confidence that that management team has in the future growth potential of Amazon even beyond just traditional e-commerce activity," said Mahn.

The all-cash deal would combine two relatively small players as Amazon continues a years-long march into U.S. healthcare, seeking to grow at a faster pace.