SANTA CLARA – Rookie linebacker Dre Greenlaw takes over for veteran Kwon Alexander, who proved in the first eight games of the season to be worth every penny the 49ers paid to acquire him as a free agent.

So as Greenlaw shifts to weakside linebacker, his approach to replacing Alexander is to not view it in those terms. Greenlaw fully realizes he cannot be Alexander, so why even try?

“It’s not about what I got to pick up or what I have to do like Kwon to go do something,” Greenlaw said. “It’s about me doing what I’ve been doing since training camp and since preseason. I feel like I bring good speed to the room, running, tackling, and I have to continue to do that. With the teammates I have, and the guys around me, that should be enough.”

Greenlaw, a fifth-round draft pick from Arkansas, has appeared in all eight games this season. He was the team’s starting Sam linebacker, a spot in the 49ers’ defense that exits the field when the club goes to its nickel personnel in passing situations.

In the 49ers’ defense, their three linebacker positions are similar, so when Alexander went down late in the third quarter last Thursday with a season-ending torn pectoral, Greenlaw was called upon to step in at the Will linebacker position.

 

“I’ve had a couple position changes,” Greenlaw said. “Last game, I had to process things a little different. I knew what they were doing, the plays they were running, but at the same time, it’s about understanding my fits.

“I was slightly more hesitant than I usually am at the Will spot. Just because the last few weeks, I’m been focused so much at Sam.”

Greenlaw had the biggest play of his rookie season earlier in the game when he tossed Arizona Cardinals quarterback Kyler Murray for a 19-yard loss on a sack. He also registered three tackles.

The assignment gets much more difficult on Monday night, as the 49ers go up against the Seattle Seahawks and Russell Wilson, the prohibitive favorite through the first half of the season to win NFL MVP. Wilson is third in the NFL in passing yards, while throwing 22 touchdowns with just one interception.

“It’s going to be fun,” Greenlaw said. “He’s a guy I looked up to, growing up watching football.”

Wilson is someone Greenlaw said he has long admired because of his ability to overcome the odds. Wilson was scrutinized coming out of college for being undersized, much like Greenlaw.

Moreover, even though they have never met, there is a connection. Greenlaw’s coach at Arkansas for three seasons, Bret Bielema, was Wilson’s coach at Wisconsin in 2011 for his final college season.

The Seahawks will almost certainly look for ways to exploit the rookie. Greenlaw said he is confident that he will not have to do too much because of the other 10 players on the 49ers’ defense, including middle linebacker Fred Warner, who lines up alongside him.

[RELATED: Insider Preview: 49ers, Seahawks set to reestablish rivalry]

“I get smarter and smarter every game, just understanding what I’m supposed to do and how things are supposed to fit, and where they’re trying to attack us,” Greenlaw said. “We really don’t know how the Seahawks are going to attack us, but the first 15 plays will show.

“For me, it’s about watching film, being prepared and just taking my assignment from the practice field to the game field and executing it there.”