Center Dan Koppen appeared to seriously injure his left knee Sunday in 9-on-7 drills, just five weeks after rejoining the Denver Broncos following J.D. Walton's setback in his comeback from ankle surgery.
Koppen, an 11-year veteran who played his first nine seasons with the Patriots, was caught in a pile early in the workout and was carted off the field and taken for medical tests.
Manny Ramirez, who took most of the snaps at center during Denver's offseason practices, stepped in for Koppen, whose teams have gone 108-28 in games he has started.
Koppen's injury is the latest setback to Peyton Manning's patched-up pocket of protection. Left guard Zane Beadles was the only starting lineman to come out of last season unscathed.