Johnson was reflecting this week on how he helped Marshall learn Denver's defense on the scout team last year when Chris Harris Jr. walked past saying, ''Next man up! Next man up!''
''Shoot, I've been here three years now. I know the system and I've been champing at the bit for a long time,'' said Johnson, who went undrafted out of Kansas, just like Harris. ''If it's time for me to go in there, I'm ready to take full advantage of it.''
Rookies Corey Nelson, who plays the nickel alongside Marshall, and Lamin Barrow also figure to get plenty of snaps after Irving tore his right MCL at New England last weekend and will be sidelined until next month.
Johnson has the most experience in Jack Del Rio's defense and the most familiarity with Marshall, who makes the defensive calls.
''Me and B-Marsh last year were on scout team together, running the whole thing. So I already know how B-Marsh plays,'' Johnson said.
Marshall joined the Broncos' practice squad a year ago after the Jaguars released him. He peppered the versatile Johnson, who plays all three linebacker positions, with questions and by season's end, Marshall had joined his old friend on Denver's 53-man roster.
''He helped me learn the defense, he did,'' Marshall said. ''I do give him credit for that and I thank him for that. So, I'm a little more comfortable being around Steve, playing with Steve. Steve's a good guy, he'll get it done.''
John Fox has joked that if there's anybody on his roster who hovers during games and implores the coach to send him in, it's Johnson.
''Pretty much,'' Johnson said with a laugh. ''I might not be standing literally next to him. But I'm always ready to go in at any position just because I love the game and I love flying around and tackling people. My speed is something that I've worked on over the years and I know I'm way fast enough to play this game and I can cover.''
Defensive captain Terrance Knighton said he expects big things out of the 237-pound Johnson, especially against the run.
''We have a lot of faith in him. He's a hitter. He's physical,'' Knighton said. ''The coaches haven't had to say, `Steve, make sure you're doing this, make sure you're doing that.' Because he prepares well anyway.''
The Broncos are accustomed to testing their depth. Last year, they lost six defensive starters on the way to the Super Bowl.
''We certainly dealt with plenty of that last year and we found a way to plug along and play effectively,'' Del Rio said. ''And we'll continue to look at it the same way.''
''That's one thing about this team: Our 2s are just as good as our 1s,'' pass-rusher DeMarcus Ware said. ''So, when they come in there and play, there isn't any lag.''
With Marshall's 60 tackles leading the team, the Broncos haven't missed Trevathan. And Marshall figures the Broncos won't miss Irving, either, even though he's second on the team with 44 tackles.
''I have faith in everybody that's in our room,'' Marshall said. ''We have a great group of linebackers and we all work hard, we're all smart, which is why we're all on the 53. So, just because they're not a starter doesn't mean that they're not capable of being a starter.''
Notes: Knighton said GM John Elway ''came in and talked to the team and let us know how he felt about the team midway through the season. He had good things to say, he had bad things to say.'' ... RT Paul Cornick (shoulder) didn't practice Thursday, opening the possibility of Chris Clark returning to the starting lineup three weeks after being benched. ... WR Demaryius Thomas needs a 100-yard day Sunday to become the ninth player in NFL history to top 100 yards in six straight games.
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