League sources told ESPN and the NFL Network on Sunday that Riddick will be sidelined six to eight weeks due to a slight fracture in his shoulder. The tailback's injury won't require surgery, according to NFL Media.
"He's got a shoulder injury and he'll miss a good bit of time," Broncos head coach Vic Fangio told reporters. "It will probably drag into the regular season."
Riddick played six snaps in Thursday's contest against the Seahawks, his first preseason action with the team. He finished the game with one carry for minus-2 yards and was targeted twice in the passing game.
Fangio said he believed Riddick sustained the injury on an incomplete pass on a fourth-and-2 late in the first quarter. Following the game, the small fracture was discovered after the Broncos returned to Denver, according to ESPN.
The Broncos have a crowded backfield that consists of Phillip Lindsay, Royce Freeman and Devontae Booker. Denver signed Riddick, a sixth-year veteran, on Aug. 4 after he visited with the New Orleans Saints and Broncos following his release from the Detroit Lions.