Marcus Mariota, like some other projected first-round NFL picks who decided to return to school, has an insurance policy that will cover him in the event of injury this season.

But at the top of the depth chart, the blindside protection coverage for Oregon's star quarterback will have to be rewritten.

Left tackle Tyler Johnstone re-tore the ACL in his right knee during the first week of fall camp and will miss the season. The 6-foot-6, 289-pound junior had started 26 consecutive games and had Mariota's back until suffering the original injury during the Ducks' Alamo Bowl win over Texas on Dec. 30.

"It's tough. Anytime you have injuries it is tough," Mariota said after Oregon completed two practices in the sweltering heat on Monday. "We understand that Tyler is going to do his best to contribute anyway he can. He's one of our spiritual leaders, he's one of those guys who can really get guys going. He understand he can use his words to be powerful and mean a lot of things.

"It is unfortunate, we're praying for him, but he's going to work back to getting healthy and he'll still make his contributions to the team."

Johnstone had vowed to return in time to continue his streak on Aug. 30 against South Dakota. Now he'll have to nervously watch Mariota's Heisman Trophy campaign from the sideline.

"I like the responsibility of being Marcus' blindside protector, I take that really seriously," Johnstone said during the spring. "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."

The coaching staff tried to stick with "We don't talk about injuries" as the official response to questions about Johnstone. However, they do acknowledge that Andre Yruretagoyena is the next man up.

The 6-5, 290-pound redshirt junior, who has played in 11 career games as a backup, has been running with the first team throughout fall camp, just as he did in the spring.

"I've seen Andre become more confident. We had a long talk about that last offseason," offensive line coach Steve Greatwood said. "I think he takes a great deal of pride in polishing his craft and working on what he has to do to improve each and every day."

On Oregon's projected preseason depth chart, Johnstone was penciled in as the starter ahead of Yruretagoyena. Elijah George, who was listed third at left tackle, and Cameron Hunt, who is expected to be the starting right guard, didn't practice on Monday afternoon, joining Johnstone in the training room.

Greatwood said junior Matt Pierson is coming on strong and true freshman Tyrell Crosby could also help with depth at tackle. Redshirt freshman Jake Pisarcik is competing at right guard.

When healthy, the versatile Hunt could also help on the outside after making his first start at right tackle last season.

"We've got a lot of good football players on this team and we're looking forward to seeing who is going to play for us," offensive coordinator Scott Frost said. "We've got a lot of good candidates to fill the job."

The Ducks will still return four starters on the offensive line from 2013 -- all-America center Hroniss Grasu, left guard Hamani Stevens, right tackle Jake Fisher and Hunt.

Still, the loss of the steady Johnstone hurts.

Mariota is already without Bralon Addison, his top returning wide receiver, who suffered a torn ACL in April.

"It's pretty sad," backup offensive lineman Doug Brenner said of Johnstone's injury. "It's an honor to play for the Ducks, and we always talk as a team that if you're out then you've got to be working your tail off twice as hard to be getting back out on the field.

"We have no doubt he's going to do that. We're not really worried about it at all, but it's a sad loss."

Follow Ryan on Twitter @rgduckfootball . Email .

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