The Rangers weren’t going to get through this postseason totally unscathed, but now their depth is really going to be tested.

The team announced Monday spark-plug winger Mats Zuccarello will be sidelined “indefinitely” with an upper-body injury, most likely a concussion. Zuccarello was hit in the left side of his head by a slap shot from teammate Ryan McDonagh with 4:30 left in the first period of Friday’s Game 5 against the Penguins, skating slowly to the bench and then to the locker room without returning.

It was a game the Rangers would win 2-1, taking their first-round series and advancing to the second round against the winner of Monday night’s Game 7 between the Islanders and Capitals. But the victory surely came at a price.

Zuccarello had spent either Friday or Saturday night at a hospital, and it’s hard to know when he might be ready to practice or play again.

“He brings a lot to the table, the way he plays, a lot of energy,” Henrik Lundqvist said. “He can open up a game with his passing. So we’re going to miss that.”

Far from a replacement, yet most likely taking his spot in the lineup, will be James Sheppard, who was a healthy scratch for all of the Penguins series. Sheppard came to the Rangers just before the trade deadline in a deal with the Sharks, and was solid — if unspectacular — in his 14 regular-season games.

“A lot of it is just — and it’s a bad habit to get into — but trying not to make the wrong play as opposed to being aggressive and making the right play,” Sheppard said after Monday’s optional practice. “The first couple games and weeks, I just didn’t want to screw anyone over or let my teammates down. So I was playing a little bit more backing off. And that’s not a bad thing, I was just looking out for my new team.”

Sheppard does have the experience of 24 postseason games, including the seven-game first-round series against the Kings last season when his Sharks blew a 3-0 lead to the team that eventually beat the Rangers in the Cup final.

“That had lots of ups and downs,” he said. “I’m just glad that [the Rangers] battled here, and I like where we’re at as a team.”

Coach Alain Vigneault said the preliminary plan would be to have Sheppard join the fourth line with Dominic Moore and Tanner Glass. Vigneault would then move Martin St. Louis up to a line with Rick Nash and Derick Brassard, and bump up Jesper Fast from the fourth line to St. Louis’ previous spot on the right next to Kevin Hayes and Carl Hagelin.

“I think sometimes guys have a plan to do more than they can do, and that’s not something that I’m looking to do,” Sheppard said. “I’m looking to do whatever I can do to contribute.”

Vigneault said there would be a forward called up from AHL Hartford at some point after their playoff game against Providence on Tuesday night. The Wolf Pack can be eliminated with a loss, down in the best-of-five series, 2-1.

“One way or the other, you need at least one spare at both positions,” Vigneault said.

Yet no matter who plays, it’s going to be very difficult to match the contributions of Zuccarello. The diminutive Norwegian had two assists in the four-plus games he played against the Penguins, and he was fifth on the team in regular-season scoring with 49 points, his 34 assists third only to Brassard and Derek Stepan.

He led the team last regular season with 59 points, and put up five goals and 13 points in 25 playoff games in the run to the Stanley Cup final.

Having just signed a four-year, $18 million contract extension, Zuccarello not only figures into this year’s picture, but into the team’s future, as well.

“We don’t know what he’s going to be back,” Lundqvist said. “We’ll just have to wait and see. He’s definitely an important player to this team.”