Irvin is expected to miss two weeks or more after suffering a sprained MCL in his right knee in last Sunday's game against the Arizona Cardinals. Irvin is one of Seattle's most versatile defenders. He plays strong-side linebacker in the team's base defense and then moves to defensive end as a pass rusher in nickel situations.
''Bruce has been playing really well and really giving us a lot of firepower,'' head coach Pete Carroll said.
It will take a three-man effort to replace Irvin in Seattle's defense. Mike Morgan will replace Irvin at linebacker while Cassius Marsh and rookie Frank Clark will pick up Irvin's snaps in pass-rush situations.
In the past, Seattle has moved K.J. Wright from the weak-side to the strong-side when similar injuries have occurred. This time around the team is electing to keep Wright at his standard position.
''We could do that but we've made the decision to go with Mike and leave K.J. (there),'' Carroll said. ''He's playing great football and I think that keeps him at his best spot and strongest spot.''
Morgan is a key special teams player for Seattle, but will be making just his second career start on Sunday against the San Francisco 49ers. He replaced Irvin for the remainder of the fourth quarter last week after Wright fell into Irvin's knee on Bobby Wagner's fumble return touchdown against Arizona.
''I've been playing in this defense for nine years (going back to USC),'' Morgan said. ''I'm excited about the opportunity to get out there and play.
Irvin's pass-rushing presence will also be missed. He's tied with Cliff Avril for second on the team with 4.5 sacks on the year. That's where Marsh and Clark will need to carry a bigger load.
Marsh missed most of his rookie season due to a broken foot and Clark is just nine games into his rookie season. Both players are still getting up to speed with the NFL game.
''You think you know so much until you get here,'' Clark said. ''Then you're humbled all over again. ... I've learned a lot of things but I'm still learning.''
Marsh and Clark have played purely on a rotational basis for Seattle this season. They have just 22 tackles combined and no sacks on the year in limited opportunities. Marsh said he's eager to get more chances this week.
''You don't complain but obviously not playing is not your favorite thing in the world,'' Marsh said. ''When you get an opportunity to get out there and shine, that's what you've got to do.''
Those opportunities haven't been as frequent because Avril and Michael Bennett have been terrific in starting roles. Both Marsh and Clark firmly understand that, but it makes them both eager to take advantage of their extra chances in Irvin's absence.
''It's obvious their role is going to be huge this week,'' defensive coordinator Kris Richard said. ''How we split up the reps has not been determined yet but those guys are going to pick up the slack.''
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