Caleb Lohner's facing an increasingly difficult battle to make the Denver Broncos' 53-man roster this summer. Even before he underwent a "routine" lower-body clean-up procedure in early June, Lohner was firmly on the team's roster bubble. Since then, Lohner (knee) hasn't been practicing at training camp, missing valuable reps as other tight ends compete for roster spots. Last week, Denver coach Sean Payton was asked if he's concerned about Lohner missing so much time. I always get a little concerned, especially if its a younger player," Payton said. "Even going through the draft or signing free agents, when we hear they might miss a portion of, you just realistically know thats a challenge then. So the sooner the better. Now I do know this, I do know what I was seeing before his injury and the work hes put in. Its interesting, when you draft someone like that, you really dont know the temperament because you havent seen enough film, and he in his first year showed us that.Lohner, abasketball player-turned-tight endout of Utah,was picked by Denver in the seventh round of last year's NFL draft. Payton praised the tight end's progress this spring, but Lohner is now falling behind. Payton said on Aug. 3 that he doesn't know how long Lohner might be sidelined. In the meantime, Nate Adkins, Justin Joly, Dallen Bentley and Lucas Krull are getting valuable reps in the tight end rotation behind veterans Evan Engram and Adam Trautman. If he's going to have a real chance of making the active roster, Lohner will need to get back on the field sooner rather than later. Social: FollowBroncos WireonFacebookandTwitter/X!Did you know:These 25 celebrities are Broncos fans.This article originally appeared on Broncos Wire: Broncos' 2nd-year tight end at risk of falling way behind in TE battle