Long before the coronavirus struck, Apple Inc.’s operations team began raising concerns about the technology giant’s dependency on China.

Some operations executives suggested as early as 2015 that the company relocate assembly of at least one product to Vietnam. That would allow Apple to begin the multiyear process of training workers and creating a new cluster of component providers outside the world’s most populous nation, people familiar with the discussions said.

Senior managers rebuffed the idea. For Apple, weaning itself off China, its second-largest consumer market and the place where most of its products are assembled, has been too challenging to undertake.

Apple’s reliance on China has long frustrated staff—and more recently unnerved investors. The coronavirus represents Apple’s third major setback there in as many years, including the fallout from tensions with the U.S. that included tariffs and slower-than-expected iPhone sales in the country.

Factory production has been crippled as China has shut down activities and sought to contain the outbreak, and Apple warned investors it won’t meet its own sales estimates in the current quarter. Since that warning, Apple’s market value has declined by more than $100 billion.