The Broncos will place center J.D. Walton on the physically unable to perform (PUP) list when training camp opens for practice Thursday. Right guard Chris Kuper is also expected to be placed on the PUP. Walton and Kuper are both battling through left ankle injuries and surgeries that didn’t take the first time. Kuper missed most of last season with his ankle injury. After a follow-up surgery Kuper is not expected to be cleared until about the time camp concludes prior to the Broncos’ second preseason game against Seattle on Aug. 17. The Broncos re-signed veteran Dan Koppen to help fill Walton’s void. There is hope Walton could return in late-October. Manny Ramirez also took the first-team reps at center during the offseason.