Already without starting right tackle Jammal Brown, the Washington Redskins lost starting left guard Kory Lichtensteiger for the remainder of the preseason Monday after he underwent arthroscopic surgery on his right knee.

And if those injuries weren’t alarming enough, backup tackle Willie Smith twisted his knee during a one-on-one drill. The second-year pro was competing to start in place of Brown but now will have an MRI exam.

The rash of injuries highlights one of the scenarios the team has worked to avoid: trying to acclimate Heisman Trophy-winning rookie quarterback Robert Griffin III to the NFL without top offensive linemen to protect him.

Despite the turmoil, Griffin maintained an even keel as he addressed the media for the first time since practices began last Thursday. He acknowledged that he keeps a close eye on the injury-related developments, but said he will not let them become a distraction.

“I definitely keep tabs on those guys and try to talk to them and see what’s going on with them, just for my mind’s sake,” Griffin said. “You definitely want to have the best guys you can have out there, but we’ve got a couple guys sitting out, and the rest of the line is stepping up and doing a good job.

“If you think that you have a banged up or bad line, then you’re going to play scared,” he added. “I don’t want those guys to think that I don’t trust them. I definitely trust my offensive line, whoever is out there with me.”

Coach Mike Shanahan also gave his healthy linemen an endorsement. He said he sees improvement in second-year pro Maurice Hurt — who took over at left tackle and also has played right tackle — and sixth-year veteran Tyler Polumbus, who has lined up as first-team right tackle with Brown out.

The Redskins are grooming third-round pick Josh LeRibeus to play either left guard or center, and on Monday signed free agent tackle Jordan Black, who has started 40 games over eight years (but only 11 in the past four seasons) with Kansas City, Houston and New Orleans.

“We do have some depth, which is nice, so if you do lose one or two guys, you’re expecting some guys to come in and fill the void,” Shanahan said.

The Redskins also lost backup linebacker Jonathan Goff for the season with a torn ACL and starting fullback Darrel Young strained his hamstring.

Lichtensteiger, who tore the ACL and MCL in the same knee last October, had practiced without limitation during the first two days of training camp, saying Friday that his knee “felt great.”

But the following day, he experienced some soreness, and received what Shanahan described as a scheduled maintenance day off. After an MRI exam, Lichtensteigher had particles removed from the cartilage in his knee.

“When you do have a little cartilage like that, and it’s this time of year, I’ve waited too many times for a week to two weeks, and then all of a sudden you go in there, right before the first game, and the guy can’t play,” Shanahan said. “I said, ‘Why not do it right now, make sure it’s OK?’ Obviously, that was my recommendation and the doctors thought it was in his best interest, so hopefully he’ll be ready to go full-speed.”

Shanahan said team doctors also examined Lichtensteiger’s previously repaired ACL and MCL, and that both are sound. In normal circumstances, Shanahan said, Lichtensteiger could return by the third preseason game. But the Redskins would rather take the cautious approach.

The coach still doesn’t know about Brown’s status. Brown will have an MRI exam on his problematic left hip on Tuesday.

Brown las week aggravated the hip injury, which has plagued him the last two seasons.

Redskins officials are counting on Griffin to infuse the franchise with life and end what have largely been two decades of failures.

Shanahan has said that Griffin, who is blessed with sprinter’s speed and a cannon of an arm, could redefine the quarterback position.

“He’s going to do things you’ve never seen quarterbacks do,” Shanahan said in May after Griffin’s first three rookie mini-camp practices.

But the coach also has stressed that the Redskins must surround Griffin with a strong supporting cast so he will have a chance to succeed.

Just four practices into training camp, that cast — particularly Griffin’s protectors — looks a bit shaky.

The Redskins also believe that with his athleticism, the quarterback could help mask some of their deficiencies on the line. In practice, Griffin has done a good deal of running, in designed and broken plays. But that carries its share of risks.

“Coach promised me he’s not going to get me killed, and we’re going to do whatever we have to do to help this team win and move the ball,” chuckled Griffin, who at 6-foot-2, 220 pounds isn’t built to take a pounding. “The guys in this league are definitely a lot bigger and a lot faster, and I experience that out here with my teammates.

“But we’re going to be smart and do it, but he said he’s not going to get me killed.”