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When asked if the 49ers were concerned that Armstead's injury might be a long-term issue, Shanahan said, "Yes, we're concerned. We do think he has a chance each week, but I'd say it's a little more the foot than the knee, something that's bothering for a little bit. I'm just hoping the pain will go down."
Shanahan confirmed that Armstead is grappling with a condition similar to the foot injury he battled through last season.
Jennings remains in the concussion protocol and could not make sufficient progress throughout the week to be ready for Monday night.
"He's made steps (through the protocol), but that's why we had to rule him out," Shanahan explained. "Just with the protocol and stuff, not enough to be able to play."