Costco shares fell 7 percent Friday on the news.
And now one trading day after Goldman Sachs downgraded Costco, another bank is following suit.
Deutsche Bank on Monday lowered its rating for Costco to hold from buy, saying the competitive advantage from its food business is at risk due to Amazon.
"The Whole Foods Market acquisition represents a game changer with Costco's competitive moat in grocery under greater threat while its digital platform lags peers, putting membership renewal at risk for decline," analyst Paul Trussell wrote in a note to clients Monday. "The pipeline of positive catalysts has played out and the competitive backdrop is intensifying with Amazon & Wal-Mart accelerating in-store and online efforts and innovation."
The analyst reduced his price target for the company to $172 from $187, representing just 3 percent upside from the Friday's close. Shares were down almost 2 percent to $163.88 during early trading Monday.
After the downgrade, seven analysts recommend buying Costco shares and now five have a hold rating. No analysts have a sell rating.