The Denver Broncos continue to deal with serious injury issues at center.
NFL.com's Ian Rapoport reported Sunday, per a source informed of the injury, that Dan Koppen is done for the season after suffering a torn anterior cruciate ligament in his left knee. Koppen was carted off the field after hearing a pop in the knee during training-camp practice.
The Broncos later confirmed the injury to Koppen, who now heads toward surgery that will end his season -- and perhaps his career.
Koppen, 33, signed with the Broncos last month after J.D. Walton was lost for the season after suffering a setback in his recovery from a dislocated ankle. Koppen filled in admirably for Walton last season, starting 12 games.
The Broncos currently are down to Manny Ramirez -- a guard by trade -- and Steve Vallos snapping the ball to Peyton Manning. The Broncos announced Sunday they had agreed to terms with Vallos, a five-year veteran, pending a physical.
Follow Dan Hanzus on Twitter @DanHanzus.