After Microsoft announced Xbox Game Pass earlier this week -- a monthly service coming this spring that will give you a selection of games you can download and play on your Xbox One for $9.99 a month, GameStop's stock price dropped nearly 8 percent. The news likely worries investors who view Xbox's instant game library a potential threat to GameStop's sales. VentureBeat reports: The brick-and-mortar retailer makes quite a lot of its money from secondhand sales where it resells products that consumers have traded in. If more people are playing digital games, that takes product out of the supply chain that could end up on GameStop store shelves. Additionally, Game Pass looks like it will primarily traffic in older games that people would typically would purchase used. Older releases like Mad Max, Saints Row IV, and Halo 5 are some of the big options that Microsoft is highlighting. Of course, GameStop isn't completely removed from the digital-gaming ecosystem. The retailer sells a lot of currency cards for the Xbox Store, the PlayStation Store, the Steam PC-gaming portal, and it's possible that people who don't like using a credit card will purchase cards to buy their subscription to Game Pass through GameStop. But that will likely not make up for a dearth of used-game sales or trade-ins if a lot of people adopt a Game Pass subscription.