The Denver Broncos will reportedly be without their starting center for the entire 2013 season.
Eleven-year veteran Dan Koppen suffered a torn ACL during Sunday's practice at training camp, according to multiple reports.
Koppen was carted off the field after being caught in a pile during 9-on-7 drills.
The Denver Post's Jeff Legwold first reported the test results after Koppen's examination.
The team later ruled him out for the season.
The 34-year-old started 12 games for the Broncos after signing a one-year deal before last season.
Denver brought him back after 26-year-old center J.D. Walton, who injured his ankle four games into the 2012 season and missed the rest of the year, underwent another potentially season-ending ankle surgery in June.
Koppen spent the first nine years of his career with the Patriots, winning two Super Bowls and earning a Pro Bowl nod in 2007.
The Broncos remaining centers include Philip Blake, C.J. Davis, Manny Ramirez and Quentin Saulsbery. Only Ramirez, who has taken most of the snaps at center during the offseason, has started an NFL game.also tore his ACL the Ravens' Dennis Pitta the Browns' Ryan Miller