James fractured a rib during Tuesday's practice, Vic Tafur of The Athletic reports.
It's a rough start to training camp for a player that some had tabbed as the favorite for San Francisco's No. 2 RB job. James should be ready well before Week 1, but missed practice time is a big deal for a player in his situation. The Niners currently have third-round pick Kaelon Black and veteran journeymen Patrick Taylor and Sincere McCormick for depth behind Christian McCaffrey.