''You don't replace the leadership,'' defensive coordinator Billy Davis said. ''You just don't. Leadership is something that is earned over time. DeMeco has got a lot of pelts on the wall and he's earned it. He's just that kind of guy. So, you're not going to replace that part of him, but we're going to have to replace him (on the field). It's the NFL, the next man has to step up.''
Ryans was lost for the season when he tore his Achilles tendon Sunday in a 31-21 victory at Houston. It's the second time in five years Ryans' season has ended with an Achilles tear. He had the same injury while with the Texans in 2010.
Matthews, the team's fourth-round pick in 2011 and Acho, who came in a trade with Cleveland last year, will split the duties in Davis' base 3-4 defense.
In base, either Matthews or Acho will play the ''Mike'' role that Ryans had and be responsible for making the defensive calls. When the team goes to its nickel or dime defenses, Mychal Kendricks will move from his ''Will'' position to make the calls.
''We have tons of confidence in both Casey and Acho,'' Davis said. ''They can make the calls. They did it all through camp when DeMeco wasn't in, or we gave DeMeco a blow. They're both highly intelligent guys. They've got a great understanding of the scheme. They've both been here for two years and both have a lot of playing time to fall back on in the regular season. So, that part to it we'll be OK with.
''It's the part that is DeMeco, the man, and his individual leadership that you're not going to replace.''
Matthews and Acho both got experience this season when Kendricks missed four games with a calf injury. In their limited time, Matthews has 24 tackles, one for a loss, with a half-sack, two quarterback hurries and a fumble recovery. Acho has 18 tackles.
Ryans had 65 tackles, three for a loss, to go with an interception and a fumble recovery.
''That helped,'' Matthews said about playing in place of Kendricks. ''It's a little different now, moving to the ''Mike'' and having to make the calls. You have to be more vocal out there.''
Matthews has played his best football of late and now has the final eight games of the regular season to show he belongs.
''It will be similar to when Mychal was out,'' Davis said. ''The neat part of our inside `backers, really within the scheme, is they are kind of interchangeable. So, it will be a similar rotation to when Mychal was out. We'll have Casey and Acho handling first and second down duties at the DeMeco spot. They'll be fine.''
Matthews knows the role he has to fill. He's as prepared as he's going to be.
''I'm ready,'' Matthews said. ''I felt when Mychal was out, I got better every week. We'll take it game by game, and hopefully get more comfortable as we go.''
Davis is confident as well.
''We've got small boxes for everybody and that's kind of the way we've had success in replacing guys,'' Davis said. ''Don't ask any one person to do everything DeMeco did, ask a couple to do a small part and really master that small part.''