Pivotal Research cut its rating on social medial giant Facebook (FB - Get Report) to "sell" from "hold," as the firm believes the company is at risk from a saturated digital ad sector as large companies analyze their marketing budgets.

"We think that the market is looking at upside potential without appropriately considering risks to growth," the firm said in a note to clients, CNBC reports. "With every passing year, digital advertising is closer to a point where the market is saturated."

Facebook's shares fell 0.6% to $171.38 on Monday morning.

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