Oakland Raiders coach Jon Gruden doesn't sound too optimistic about the injury to guard Gabe Jackson. Jackson, Oakland's starting right guard, went down during team drills at Thursday's practice.

“We’re concerned, obviously,” Gruden said after practice, via Scott Bair of NBC Sports. “We’re really concerned. We’ll get more information that will allow us to be specific with you.”

The fact that Gruden said concerned twice doesn't seem to bode well.

“He just got rolled up,” Gruden continued. “We’re hoping he’s okay.”

While it's too early to speculate about what kind of injury Jackson is dealing with, it definitely doesn't sound like something super minor. When asked about what the team might do at right guard while Jackson is out, Gruden said no decisions have been made.

“We'll have to put our heads together,” Gruden said. “And take a look at where we're going if Gabe isn't available.”

This is especially unfortunate news for the Raiders because they're already down one starting guard. They signed Richie Incognito earlier this offseason to start at left guard, and he's suspended for the first two games of the season. Oakand recently brought in Jonathan Cooper to hold down the fort while Incognito is suspended, and it might have to add another veteran guard.

If Jackson, a starter since he entered the league in 2014, is forced to miss any regular season time, it'd be a huge blow. Jackson is one of the league's better guards, and the Raiders' offensive line will be pretty thin without both him and Incognito.