The stock price of the New York-based cable company, which just launched a wireless mobile unit as it grapples with cord-cutting, plunged 20.62% to $24.89 after it reported a significant decline in core video revenue.
Revenue from its pay-TV/video segment, which generates 41% of the cable company's revenue, fell 5.8% to $993.1 million.
Altice also cut its guidance for full-year 2019, saying it now expects revenue growth of 2.5%, down from its previous forecast of 3% to 3.5%.
The cable giant's quarterly results fell short of analysts' expectations for earnings and revenue.
Altice reported net income for the quarter of $77.2 million, or 12 cents a share, compared to the 15 cents analysts had expected.
At $2.44 billion, revenue just missed the $2.48 billion analysts had expected.
Still, analysts Wednesday shrugged off the earnings fizzle by Altice to take a long view of the cable provider's prospects.
Of the 31 analysts who cover Altice, 23 have buy ratings on the stock, seven have holds, and one has a sell, according to a survey by Bloomberg News.
While acknowledging a "mixed" third quarter, Wells Fargo analyst Jennifer Fritzsche attributed the results to one-time promotion roll off and costs associated with the launch of Altice Mobile.
Those factors "should reverse in FY2020, which makes us confident" in top-line growth next year," the Wells Fargo analyst wrote.