ENGLEWOOD—Just when it appeared Adam Gotsis was making major improvement.

The Denver Broncos’ second-year defensive lineman did not attend the team’s final offseason practice Thursday as he will undergo an arthroscopic surgery to determine the cause of knee pain, a player source told 9News.

Gotsis was the Broncos’ second-round draft pick out of Georgia Tech last year. His rookie season was limited as he was overcoming surgery to repair a torn ACL suffered during his final season at Georgia Tech.

Gotsis was noticeably stronger and more active up front during the offseason.

The Broncos have suffered three significant injuries this season, all to backup defensive players. Outside linebacker Shaq Barrett has been down with a hip injury and defensive tackle Kyle Peko will be out at least six weeks with a broken foot.