Dick's Sporting Goods shares have already been cut in half this year and things are about to get worse, according to one Wall Street firm.
Cowen lowered its rating on the retailer to market perform from outperform, saying it will suffer as suppliers such as Nike and Under Armour increasingly sell directly to consumers online.
"Despite Dick's Sporting Goods remaining the preferred destination when shopping for sporting goods according to the Cowen Consumer Tracker, slowing N. America sales growth rates from key vendors Nike and Under Armour, along with increased emphasis on the brands' own direct-to-consumer platforms will pressure Dick's Sporting Goods SSS [same-store sales] growth and margin profile," analyst John Kernan wrote in a note to clients Thursday.
"Competing with Amazon is too difficult … Amazon continues to gain share," he added.
Dick's Sporting Goods shares are underperforming the market this year. Its stock is down 50 percent year to date through Wednesday versus the S&P 500's 9.2 percent return.
The retailer on Aug. 15 reported weaker-than-expected second-quarter earnings results and lowered guidance for the year.
Kernan reduced his price target for Dick's Sporting Goods to $28 from $31, representing 5.5 percent upside from Wednesday's close.
He said Nike and Under Armour represent 20 percent and 12 percent of Dick's Sporting Goods sales, respectively, which is a problem because these key suppliers will increasingly sell through other distribution channels.
"With Nike's plans to shortly begin direct selling on Amazon, Dick's Sporting Goods likely three largest vendors, Nike, Under Armour and Adidas will all be selling directly on Amazon," he wrote. "Sporting good and athletic apparel and footwear industries are currently over-inventoried and the environment is as promotional as we have ever seen."
Dick's Sporting Goods did not immediately respond to a request for comment.
— CNBC's Michael Bloom contributed to this story.