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The 49ers picked up the fifth-year option on Arik Armstead‘s contract, but it’s guaranteed only for injury. The defensive lineman has much to prove this season, in his fourth season, after missing 18 games over the past two years.

The 49ers know it. Fans know it. He knows it.

“For sure,” Armstead said, via Matt Maiocco of NBC Sports Bay Area. “I’ve been hurt two years in a row, so that brings a lot of, ‘What are you going to do?’ So definitely [I] have a lot to prove and look forward to having a healthy season, and I know what I’m capable of if I’m on the field.”

Armstead ended the past two seasons on injured reserve, needing shoulder and hand surgeries. As a rookie in 2015, he played 16 games but started only one after the 49ers made him a first-round pick.

“Of course, there are critics,” Armstead said. “Of course, fans want players to be out there and not be hurt, but part of football is being injured. I can’t control that. All I can control is, if I do get hurt, I try to rehab and get back healthy and play to the best of my ability.”

Armstead will line up at the “big end” spot after formerly playing on the other side as the pass-rushing “Leo.” He will play defensive end in the base defense and move to defensive tackle in the team’s substitution packages.

“Arik’s going to do a lot of things for us this year,” 49ers defensive line coach Jeff Zgonina said. “I think he’s more comfortable this year than last year. We tried him at a few spots last year, and I think he’s really starting to feel comfortable at that big end spot and inside pass-rusher on pass downs. I think he has more of a defined role.”