McCoy was hurt late in the practice. He was face-down on the field for several minutes before limping to a cart.
Seattle coach Pete Carroll said the initial diagnosis is that McCoy's injury is significant and that it's on the opposite leg of a previous torn Achilles that cost him all of last season. McCoy injured the Achilles on his right leg during offseason workouts before the 2013 season.
This article originally appeared on FOXSports.com