Apple CEO Tim Cook delivers a keynote during the European Union's privacy conference at the EU Parliament in Brussels, Belgium October 24, 2018.

Apple shares fell Tuesday after HSBC downgraded the stock, citing too much dependence on a single product and slowing emerging markets economies.

HSBC downgraded Apple to hold from buy and cut its 12-month price target to $200 from $205. Apple shares fell 1.7 percent to $181.66 shortly after the opening bell Tuesday, adding to an 18 percent decline already for this quarter.

The note from the HSBC analysts said:

"Apple's iconic hardware unit growth is broadly over for now. Revenues are only supported by higher selling prices and by the development of services. Flat unit growth has hit Apple's share price and incidentally its key suppliers. What has made the success of Apple, a concentrated portfolio of highly desirable (and pricy) products is now facing the reality of market saturation."

HSBC also went into an in-depth analysis of whether Apple should trade at a higher earnings multiple in line with stocks that sell luxury goods. It concluded that Apple's shares are not "particularly expensive" but don't deserve a higher multiple associated with luxury brands.

And if its multiple won't expand, there isn't any other way to justify a higher stock price since earnings and revenue growth are likely to slow, the analysts said.

"As Apple moves from very high double-digit revenue growth to a more pedestrian mid single-digit (both top and bottom line), the slowdown in the second derivative of growth will weigh on the stock's investment case," the note said. "While we understand the company's interest of not disclosing unit sales of hardware and focusing more on service gross margin, investor enthusiasm could be the victim of a lengthy transition phase as the focus shifts."

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