ENGLEWOOD, Colo. (AP) -- The Denver Broncos' top-ranked run defense suffered a potential body blow Wednesday when weakside linebacker Danny Trevathan was carted off the field with a knee injury toward the end of practice.
There was no immediate word on the severity, but there was considerable concern it was serious.
"It was really tough," fellow linebacker Steven Johnson said. "I mean, when I see Danny go down, we all walked over to him. Practice kind of came to a halt for a good three to five minutes, and we were sitting there, just kind of praying for him."
Coach John Fox only mentioned the second-year linebacker in passing when rattling off injuries after practice, saying Trevathan was "limited, knee."
The loss of Trevathan would be a big blow to the Broncos (4-0).
According to Pro Football Focus, he was the league's top 4-3 outside linebacker against the run in the first month of the season.
He's second on the team with 30 tackles and 24 unassisted tackles and has a sack, an interception and four pass breakups so far.
Trevathan, a second-year pro from Kentucky, worked his way into the starting lineup this summer when the Broncos moved Wesley Woodyard to middle linebacker and inserted Nate Irving on the strongside with All-Pro Von Miller having to sit out the first six games on a drug suspension.
Johnson is listed as Trevathan's backup.
"You never want to see anybody go down, but somebody has to step up and somebody has to fill that void," Johnson said. "Like I told Wood after practice when we were walking off the field, I was like, `Look, man. If I get the opportunity to go in that game, I will not let you down.' He was like, `I know you won't. I know you won't."'
Johnson has only played one snap from scrimmage this season while logging 110 plays on special teams, including a blocked punt which he recovered himself for a touchdown against Philadelphia last week.
"I think he'll be able to step in," Irving said. "He knows everything. It's something that the coach tells us to pride ourselves on: being able to be plugged into any position and just keep playing. And if that's the case, I think he'll do OK."
Johnson, a second-year pro who went undrafted out of Kansas, has never recorded a tackle from scrimmage in his 15 games for the Broncos, although he tied for the team lead with 10 special teams tackles last season and is their leader again this year with four.
He said he'll make sure Denver's run defense doesn't miss a beat if he's pressed into starting duty Sunday at Dallas.
"That's just how I played in college: I always played with my heart and left it all out on the field," Johnson said. "I mean, whatever happens, happens. I'm hoping and wishing the best for Danny. I just hope that if I do get in, I can make an impact for this team."
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