After 15 weeks of stability and health along the offensive line, the Washington Redskins face the possibility of having to replace two starters as they prepare for one of their most important games in years, Sunday’s contest in Philadelphia.

To complicate injuries sustained by two starters on Sunday against the Cleveland Browns, the NFL announced that one of the team’s top backup linemen, Jordan Black, has been suspended for using performance-enhancing drugs. The announcement came Monday.

Coach Mike Shanahan said that right tackle Tyler Polumbus, who sustained a concussion in the first half of Sunday’s 38-21 victory over the Browns, will continue to be monitored throughout the week.

The coach declined to provide an update on the health of center Will Montgomery, who has a sprained medial collateral ligament in his left knee. Montgomery sustained the injury late in Sunday’s game and did not return after he was checked on the sideline by medical staff.

Shortly after Shanahan’s Monday afternoon news conference, the team issued a statement from the NFL that Black, who played the entire second half Sunday in place of Polumbus, has been suspended for four games.

The Washington Redskins backup QB Kirk Cousins leads the team to their fifth straight win in a row to put them on top of the NFC East igniting playoffs hopes in the Washington region. (The Washington Post)

Taken together, the news put one of the team’s most stable units in a suddenly precarious situation as the Redskins try to win their final two games and capture the NFC East title for the first time since 1999.

The Redskins closed out the game with Kory Lichtensteiger (usually the starting left guard) at center and backup Maurice Hurt at left guard. Shanahan said, “We’ll talk about Will more on Wednesday,” but added that the team is well prepared at center with Lichtensteiger, right guard Chris Chester and rookies Josh LeRibeus and Adam Gettis both able to play that position if Montgomery can’t.

The options at right tackle aren’t so plentiful.

Polumbus had started all 14 games after Jammal Brown was lost for the season with recurring hip injuries.

Polumbus could play Sunday if he shows no lingering symptoms and passes tests throughout the week. (Teammates Robert Griffin III, Aldrick Robinson and Josh Wilson all suffered concussions during games earlier this year but recovered in time to play the following week.)

If Polumbus is unable to play, the Redskins must decide whether to go with Hurt, a second-year pro who started eight games at left guard last season and has seen time at tackle in practices, or rookie Tom Compton, who spent the first 13 weeks of the season on the practice squad before he was promoted to the 53-man roster two weeks ago.

Asked about his level of concern regarding the line, Shanahan expressed confidence in the healthy players on the roster.

“We’ve got a little more depth,” Shanahan said, referring to improvements over last season, when injuries along the line helped trigger a six-game losing streak that followed a promising 3-1 start. “We’ve got a few guys that are draft choices that have been working extremely hard and understand our offense, and if put in — if they need to play — I think they’ll do an excellent job.”

Entering the season, the health of the offensive line, and its ability to protect Griffin, ranked among the Redskins’ biggest concerns.

In addition to Brown’s injury, Williams injured his foot in the preseason opener and missed time and Lichtensteiger, who was returning from tearing the ACL and MCL in his right knee in 2011, had arthroscopic surgery on the same knee and didn’t play a preseason game. Chester also missed time during the preseason with an ankle injury.

At one point during training camp, Griffin lined up behind a line that featured only one projected starter: Montgomery. Once the season began, however, all but Brown made it back into the lineup.

The Redskins have one of the NFL’s best offenses this season. They are fourth in total yards, first in rushing and fifth in points. The line has led rookie running back Alfred Morris to 1,322 yards rushing — third-most in the NFL — and helped him set franchise rookie rushing records. Even without the second running threat offered by Griffin on Sunday, the line fared well against Cleveland. After struggling early, the unit regrouped and played better from the final possession of the first quarter to the end of the game.

Williams has played through knee, ankle and thigh injuries and has remained effective. Until now, however, the rest of his linemates had avoided serious injuries.

The Redskins won’t know until later this week just how battered the unit will be Sunday.

But Lichtensteiger, who had spoken to both Montgomery and Polumbus, said he is optimistic that disaster can be averted.

“I don’t think we’re necessarily going to have to shuffle everything around,” he said. “I don’t know how serious everything is, but when I left the bus, on my way home, I felt like everybody was pretty confident that they could give it a shot this week.”

Even if Montgomery and Polumbus can’t play, Lichtensteiger said he shares Shanahan’s optimism about the team’s overall depth.

“It’s not like these combinations of people have never played together,” he said. “We do get practice reps together. Those second-team guys cycle in to give guys breathers. Everybody does a pretty good job in practice, and I think we all know what we’re doing. They have the timing down of our offense pretty well. I’m not too worried about the scenario, whoever is in there.”