The sight of defenseman Matt Niskanen gingerly walking down the tunnel and to the locker room Wednesday night in Philadelphia forced the Washington Capitals briefly to consider one of their bleakest scenarios. Niskanen had suffered an undisclosed “lower-body” injury when his left leg collided awkwardly with Flyers defenseman Radko Gudas, and Niskanen was later ruled out for the rest of the game.

Washington has been fortunate to avoid serious injuries on the blue line this season, and it again received a break when the initial prognosis on Niskanen’s ailment suggested a short recovery. But with the NHL trade deadline less than a week away and the Capitals again in position to contend for the Stanley Cup, the injury scare to the all-situations blue-liner raises some concern over the team’s defensive depth..

If he or fellow right-handed shot John Carlson were injured in the postseason, would Washington be able to cope without one of their top two defensemen? Should General Manager Brian MacLellan consider shoring up that area before the Wednesday deadline with a blue-liner who could handle top-four responsibilities? How much to tinker with the NHL’s first-place team for the sake of injury protection will be what MacLellan wrestles with most this week. At this point, the Capitals appear more likely to stand pat than make another move.

“I think it’s always tough because, ideally, you just like to go with what you have, but if someone gets hurt, it’s like, ‘Well, why didn’t you get someone?’ ” MacLellan said. “I mean, you’re always going to be opening yourself up to that. . . . We don’t have a specific need that we’re trying to address. We’re trying to just say, ‘If something happens, what’s the best way to cover that?’ The insurance.”

Niskanen’s injury might keep him out of the lineup for a handful of games, but with the Capitals comfortably atop the standings, he can take his time healing before returning to the lineup. Defenseman Brooks Orpik didn’t practice Thursday because he took a maintenance day for a lower-body injury, and he’s questionable to play Friday against Edmonton.

If there’s a silver lining to Niskanen and potentially Orpik both being out, it’s that Washington will have an opportunity to examine how its depth players handle more responsibility. The team acquired right-shooting defenseman Tom Gilbert from the Kings last week as veteran insurance, but Capitals Coach Barry Trotz said he wants Gilbert to play more with the American Hockey League team, so Aaron Ness was recalled. With Ness, the team has six left-shooting defensemen on the roster.

Defensive depth arguably hurt Washington in the playoffs last year. Orpik was suspended for three games in the second round, and Trotz didn’t seem to trust Dmitry Orlov or Nate Schmidt in a postseason top-four role, causing lineup turnover in the Capitals’ series loss to Pittsburgh. MacLellan and Washington’s coaching staff are most encouraged by Orlov’s and Schmidt’s improved play this season and expect them to handle the playoffs better this time around. Orlov has shined in a top-four role all season, and Schmidt has played primarily on a third pair with Orpik.

But if someone in the team’s top four were to get injured or face a suspension, as was the case last year, is there an easy internal fix?

“I don’t know that we have a top-four upside,” MacLellan said. “I think we have guys that can fill in for periods of time. I think Orpik can move up to the top four if we needed him. Schmidty maybe for a period. I don’t know that it’s a long-term solution. Everything would be temporary as far as top four goes.

“. . . I think it concerns every team. I mean, nobody has five, six top-four defensemen. You have four, you have three, and you work around those three or four. The good teams have four.”

MacLellan argued that a No. 1 defenseman such as Niskanen or Carlson can’t be replaced with a pending unrestricted free agent deadline addition, and Washington is not looking to make any blockbuster deals. “We’re not going to mess with lines or defense pairs. If we could upgrade on the fringes, we might do it,” MacLellan said. The Capitals are also limited in available salary cap space: The website Cap­ projects Washington will have roughly $1.12 million in annual cap hit available at the deadline.

On Thursday morning, the Penguins, with blue-liners Trevor Daley, Olli Maatta and Justin Schultz all out with injuries, acquired defenseman Ron Hainsey from the Carolina Hurricanes. MacLellan said the moves of division rivals don’t influence his decisions, though he’s certainly monitoring them. He also has observed that the trade market for defensemen is restricted by the looming expansion draft because just three can be protected and acquiring one now might mean losing another in June’s draft.

MacLellan believes this is the best team that has surrounded stars Alex Ovechkin and Nicklas Backstrom, and there’s a sense of urgency with the Capitals having 10 players up for new contracts this summer, meaning the team inevitably will look different next year. Though the indication is that the trade deadline will be quiet in Washington, MacLellan feels the same pressure to leave no stone unturned before an all-in postseason.

“I have to do my job,” he said. “I have to pursue anything that I think can be a possibility that might make us better, and when we get down into the nitty-gritty, you say yes or no. And it’s going to be based on what effects it’s going to have on our team.”