Cook tells investors that the majority of revenue shortfall is due to slowing sales in "Greater China", which the company defines as China, Hong Kong, Macau and Taiwan, but goes on to mentioned China's trundling economy as one of the biggest contributing factors to forecast cuts.
Cook attributed most of the revenue drop to China, where the economy has been slowing and where USA tariffs have been raised on more than $200 billion in goods, although the iPhone hasn't been affected directly so far.
That figure is 4.8% below the $88.3 billion revenue in the same quarter a year earlier.
"While we anticipated some challenges in key emerging markets, we did not foresee the magnitude of the economic deceleration, particularly in Greater China", Cook wrote.
Apple also admitted that selling newer, pricier iPhones has been challenging across emerging markets in Asia. He said the company was performing strongly outside of the communist nation.
Apple is now the highest-profile multinational corporation to warn that the economic slowdown in China could hurt its business. "This turned out to have a significantly greater impact than we had projected".
Cook also spoke of "rising trade tensions with the United States" which has seen Apple become the target of a boycott campaign by prominent Chinese companies, something which has escalated more when Huawei's CFO was arrested in Canada. In response to the news, Apple's stock fell eight percent in after-hours trading yesterday and remains down since the markets opened today.
New Zealand share prices edged lower following on from another volatile session on Wall Street, which saw the Dow Jones industrial index drop by 2.8 per cent on the back of a profit warning from the USA tech giant Apple. The CEO also mentioned that Apple is expected to report a new all-time record for Apple's earnings per share.
But most of those new Samsung smartphones, as well as those from Apple and other OEMs, will likely cost more than what many are willing to pay.
Wedbush Securities analyst Daniel Ives described it as "Apple's darkest day during the Cook era", saying: "No one expected China to just fall off a cliff like this".
Further, Apple expects a gross margin of about 38 percent, along with operating expenses of approximately $8.7 billion ($11.8 billion), according to a press release from the company.