Oakland Raiders offensive guard Gabe Jackson was carted off the field with a leg injury during Thursday's joint practice with the Los Angeles Rams.
ESPN'sPaul Gutierrez noted Jackson was later spotted wearing a brace on his left knee and using crutches, though the severity of the injury is not yet known.
"We're concerned, obviously," Oakland coach Jon Gruden said, per Gutierrez. "Really concerned about him. But we'll get more information here and we can be specific for you. I don't want to speculate. Unfortunate. Hope he's OK."
This article will be updated to provide more information on this story as it becomes available.