Apple has warned investors about its growth in the most recent quarter, citing weaker sales in China.
In an unexpected disclosure, the iPhone maker said it expected revenue of about $84bn (£67bn) in the three months to 29 December.
That is down from its November forecast of at least $89bn - a prediction that had already disappointed investors.
The firm's shares have already fallen more than 28% since it offered investors that outlook.
"While we anticipated some challenges in key emerging markets, we did not foresee the magnitude of the economic deceleration, particularly in Greater China," he said.
"In fact, most of our revenue shortfall to our guidance, and over 100% of our year-over-year worldwide revenue decline, occurred in Greater China across iPhone, Mac and iPad."