This wasn't a week to remember for Korea-based e-commerce specialist Coupang's (CPNG -1.77%) shareholders. According to data compiled by S&P Global Market Intelligence, from last Friday's close to this one, the stock declined by almost 11%. But that wasn't surprising, considering that a researcher from a top U.S. bank downgraded his recommendation on the shares.

Citigroup downgrades Coupang to neutral from buy

Specifically, this was Citigroup's John Yu, who on Tuesday before the market open changed his rating on Coupang from buy to neutral. Accompanying that, he also enacted a 15% cut to his target price on the stock; it now stands at $17 per share, from the prior level of $20. In his research note detailing the change, Yu cited the e-commerce company's recent purchase of high-end fashion purveyor Farfetch Holdings and the ramp-up of its operations in Taiwan as major tailwinds.

In mid-December, Coupang heralded the $500 million deal for Farfetch. Management has promised to "rededicate" that business "to providing the most elevated experience for the world's most exclusive brands, while pursuing steady and thoughtful growth as a private company." Earlier in the year, it said it would accelerate its investments in Taiwan, which is one of the great economic success stories in Asia.

Skepticism abounds

Neither of these moves has impressed investors, who for the most part have traded Coupang stock down since the news items were published. Analysts are also clearly skeptical about both its prospects in the hot Taiwanese market, and of the synergy with Farfetch. Coupang management will have to develop one or both to the point where they clearly benefit the company's business.