Apple Inc. shares stumbled Friday as investors fretted over the iPhone maker’s financial outlook for the important holiday quarter and the company’s decision to stop reporting device unit sales in future results.

The stock fell 6.6% to $207.48, its worst percentage decrease since January 2014 and a drop that nearly knocked Apple from its lofty trillion-dollar stock-market valuation. Technology stocks, particularly those with sky-high valuations, have slumped in recent weeks.