Roku fell more than 9% on Wednesday after MoffettNathanson analyst Michael Nathanson downgraded the stock.
Nathanson gave the stock a sell rating and a $220 price target, representing a 20% drop from Tuesday's finish of $276.46.
Roku's stock is now trading at roughly $251.51.
In a research note to investors, the analyst stated that the stock's underperformance prompted them to examine their model's basic assumptions more closely.
"To put it plainly, we believe our and the Street's long-term revenue and earnings projections are simply too damn high," Nathanson said.
"It appears that Roku will have to monetize an unrealistically high percentage of long-tail AVOD impressions to even come close to Street projections," he said. "We believe this will be a struggle given escalating competitive pressures in TV OEMs and operating systems."
Roku's stock has dropped by more than 21.6% this year.