EUGENE — Offensive linemen are the secret service agents of football.

EUGENE — Offensive linemen are the secret service agents of football.

The job description includes safeguarding their leader from defensive players coming after the quarterback with bad intentions. The general public usually only notices these anonymous giants when something goes wrong.

Oregon left tackle Tyler Johnstone is motivated to return to duty from a torn ACL in time for the 2014 season, because he knows a healthy and well-protected Marcus Mariota could deliver the program's first Heisman Trophy and national championship.

"I want to be the guy out there, obviously. I like the responsibility of being Marcus' blindside protector. I take that really seriously," Johnstone said. "It's hard to trust someone else with that responsibility, but I do have a lot of trust in the guys backing myself and the rest of the starters up.

"Whoever is in the game, they're going to get the job done and we're all confident about that."

If Johnstone's surgically repaired knee isn't quite ready for the rigors of the season by Aug. 30, when the Ducks open against South Dakota at Autzen Stadium, Andre Yruretagoyena will be ready to start in his absence.

Yruretagoyena, a 6-foot-5, 284-pound redshirt junior who appeared in seven games last season, has elevated his play during spring practices while getting first-team reps at left tackle.

"I'm just learning as much as I can and playing as hard as I can," Yruretagoyena said. "Hopefully, I can earn a starting job or at least have a pretty big contributing role this season."

Yruretagoyena, a four-star recruit coming our of Chaparral High in Scottsdale, Ariz., arrived at Oregon with the talent to play at the Pac-12 level. Recently, he has made significant strides in the weight room and played to the standard veteran offensive line coach Steve Greatwood requires.

"I really like where Andre is right now. I'm starting to see him play with a demeanor that I expected from him all along," Greatwood said. "He's got a little bit of a swagger to him out there, he knows what he's doing and he busted his tail in the offseason.

"So he's stronger and more physical than he's ever been. I'm excited about the growth that he has put in, really just in this last winter and into the spring."

Because of a combination of injuries, graduation and recruiting misses, many programs have a difficult time piecing together enough offensive linemen for a spring game.

The Ducks will return all five starters from last season when Johnstone is recovered. The unit also has a strong second wave pushing for playing time during these 15 spring auditions.

Redshirt juniors Matt Pierson and Jamal Prater, junior college transfer Haniteli Loisi, redshirt sophomore Matt McFadden, and redshirt freshmen Doug Brenner, Jake Pisarcik and Evan Voeller are all competing for spots in the rotation. Redshirt freshman Elijah George is currently out with an apparent knee injury.

"Our older guys have to be able to look and say, 'Wait a minute, if I'm not giving my max, one of these younger guys is going to step up and push me and beat me out,'" Greatwood said. "It's nice to have that. Competition is the greatest thing a coach can have. I feel like we're getting to that point."

Yruretagoyena said he doesn't necessarily look at the situation as a chance to compete for Johnstone's starting job. The two have been friends since childhood.

"We're not big spotlight guys, so even if I'm just getting in there as a rotation guy, it doesn't matter," Yruretagoyena said. "I just want to help with the offense. I think just knowing there's a lot of competition motivates all of us to keep battling every day."

Three of the incumbent starters — left guard Hamani Stevens, all-America center Hroniss Grasu and right tackle Jake Fisher — are seniors. Right guard Cameron Hunt started as a freshman, and the coaches are also very high on his classmates who redshirted last season.

"They are quick learners, I'll be the first to admit. Obviously it has taken me awhile to get into the rotation and I'm still working for that," Yruretagoyena said of the offensive linemen from the 2013 recruiting class. "They're a lot brighter than I was when I was a freshman, I'll just say that. They're a bunch of great kids. They've pretty much all latched onto somebody and taken to heart what the older guys have said."

Yruretagoyena isn't just competing at left tackle. He has learned every position on the line except for center.

"We're all counting on the fact that Tyler is going to be there. Andre could end up anywhere," Greatwood said. "That's what it's all about. I'm going to get my best five out there."

Johnstone, who was injured in the first half of the Alamo Bowl on Dec. 30, is still out on the field with the Ducks for every practice. He hasn't been cleared for contact drills but believes he will be ready for fall camp in August.

For now, Johnstone is enjoying the progress Mariota's current blindside protector is showing.

"I think it took Andre awhile to get the aggressive mindset that it takes to be a Division I college football player. That's what has kind of been noticeable this spring ball for him, he's just really come around," Johnstone said. "If he makes a mistake he doesn't get down on himself, he just forgets about it, moves on and tries not to make the same mistake again. He's just a lot more competitive. It's kind of fun to watch."