"Given the lower sales expectations resulting from softer demand for the company's underlying products, we are lowering our rating to," the firm wrote in an analyst note.
"While we continue to believe in the company's products and longer term strategy, the underlying variability of its financial model and lack of visibility into new products have forced us to appropriately reflect this risk within our rating," Barclays added.
During the quarter, Fitbit shipped its new products earlier to its retail partners in anticipation of the holiday season, which shifted some revenue into the third quarter from the fourth quarter, the firm noted.
Additionally, the backlog of shipments led to higher accounts receivables, Barclays said.
Shares of Fitbit were higher in pre-market trading today.
Separately, TheStreet Ratings Team has a "Sell" rating with a score of D+ on the stock.
This is driven by multiple weaknesses, which should have a greater impact than any strengths, and could make it more difficult for investors to achieve positive results compared to most of the stocks covered.
Among the areas that are negative, one of the most important has been unimpressive growth in net income over time.