SANTA CLARA – Defensive lineman Arik Armstead, who has not suited up for an exhibition game this summer due to a shoulder injury, believes he will be ready for the 49ers’ regular-season opener.

Armstead declined to discuss the specifics of the injury – other than to say it’s not a bruise. But he did say there remains the possibility the injury could require surgery in the future.

“It may. It just depends,” said Armstead, whose left shoulder was wrapped in ice. “I feel good right now. Just keep my maintenance up with it. I’ll be fine.

“I’m not worried. I think I’ll be fine, just stay on top of it and keep my maintenance up.”

Armstead, the 49ers’ first-round draft pick of last year, was lining up with the 49ers’ first-team defense before he sustained the shoulder injury during practice on Aug. 7. He is not expected to suit up for the 49ers' preseason finale Thursday night against the San Diego Chargers.