BOSTON — For the better part of five months, the Lightning was lucky. The injuries that pile up in the course of a season didn’t seem to affect it much.Sure, goalie Andrei Vasilevskiy was out for a month with a broken foot. But Louis Domingue stepped in nearly seamlessly.Even when defensemen Dan Girardi and Anton Stralman got hurt a month ago — Stralman out for 12 games and Girardi possibly returning for Saturday’s regular-season finale against the Bruins — Jan Rutta stepped in smoothly. But then Victor Hedman failed to emerge from the dressing room for the second period last Saturday against the Capitals, and he hasn’t played since, out with what the team has called only an upper-body injury.An inadvertent headbutt — Capitals wing Carl Hagelin caught Hedman with a helmet to the chin while Hedman delivered a hit on the boards — sent fans into a panic. Some reacted angrily about the Lightning not resting players and more with concern about what this would mean for the Lightning’s season.Hedman did not practice Friday and will not play today. Coach Jon Cooper hopes Hedman will be available for the playoffs, which start Wednesday (the entire first-round schedule will be announced Sunday).After today, Hedman will have missed 4 2/3 games. Ideally a player gets a few days of practice after a week off the ice. Cooper said he expected Hedman back Monday and would assess from there.So Hedman could rejoin the team immediately upon the return to Tampa from this road trip and have no issues being in the playoff lineup from the first puck drop. Four-plus games off would mean some adjustments to his first game in at least 11 days, depending on when the Lightning’s first game is, but nothing major.But what if he’s not ready to go then? What does the Lightning look like if Hedman misses at least part of the playoffs?“Victor plays a big role on our team,” defenseman Ryan McDonagh put it plainly. “Everybody has to try to do a little bit more here.”The reigning Norris Trophy winner as the league’s top defenseman plays in all situations. He plays the point on the power play (Cooper called him the driving force) and is on the penalty kill. That’s a lot to replace. Without Hedman, Cooper said, you can’t take some things for granted.“He can make up for a ton of mistakes that happen,” Cooper said. “You throw every cliche in the book of ‘next guy up’ or spread the minutes around, but it’s a big loss for us.”Enter Mikhail Sergachev. With Stralman and Girardi injured, Sergachev moved to their shared spot in the top defense pairing with Hedman. Now he’s taking on some of Hedman’s responsibilities, including playing point on the first power-play unit. That unit has been potent for the Lightning all season, and Hedman, though his statistics don’t necessarily reflect it, has been a big part of it.There typically aren’t as many power plays in the playoffs, so the ones a team has become more important. Braydon Coburn, who has played most of the year with Sergachev, isn’t worried. “(Sergachev has) manned the second unit all year long,” Coburn said. “He knows what he’s doing. He’s got a great shot from the point as well. I think teams have to respect that.”Having spent the past few weeks paired with Hedman has given Sergachev confidence. He’s feeling it and displaying more skill.Sergachev has grown throughout the season. He has shown himself to be a player who thrives with more responsibility. The more minutes he plays, the more situations he plays in, the better he looks. He makes it sound simple: It’s all about confidence.Early in the season, Sergachev didn’t get a lot of ice time and wasn’t often put out against tough lines. That has changed, especially in the past few weeks. McDonagh thinks it has been good for Sergachev.“He’s been up for the challenge,” McDonagh said, “playing physical, playing in their face, not allowing his offensive game to slip even with the bigger defensive responsibility.” Contact Diana C. Nearhos at firstname.lastname@example.org. Follow @dianacnearhos.