They’ve always been the ones Jack Capuano didn’t need to worry about. Matt Martin, Casey Cizikas and Cal Clutterbuck make up one of the most formidable fourth lines in the NHL, and with one exception, they’re the Islanders most potent scoring threat — gritty cousins to John Tavares’ ever-dependable skill line.

They’re rarely separated, sparingly criticized, but on Wednesday night, Capuano and company couldn’t deny the fact that’s been staring the Islanders in the face since these playoffs started: The trio is in trouble.

“They’re fighting it right now,” Capuano said. “It’s no question. They’re fighting it.”

The result is something not often seen during a game, unless there’s an injury: Martin skating with Ryan Strome, or Clutterbuck with the kids, Shane Prince and Adam Quine. That’s what happened in the second period after a lackluster showing in the first — one that saw the Islanders firmly on their heels despite the scoreless frame — as the third and fourth lines were jostled in a desperate attempt to get something going.

With the series against the Panthers now tied 2-2, the fourth line has mostly been a non-factor. None of the three have registered a point and they’ve managed a combined 24 penalty minutes. In the Islanders Game 3 overtime winner, both Clutterbuck and Martin registered at minus-3, while Cizikas was minus-2. Cizikas was called for tripping in the first period Wednesday, while Martin got hooked for the same penalty in the second — the latter leading to the Panthers’ opening goal in the eventual 2-1 victory.

“It was going to be a fight and I think we knew it,” Martin said. “I thought we [as a team] played a lot better in the second and third but it takes a full 60 minutes to play this time of year and we need to play a lot better.”

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Capuano seemed confident that his veterans would get it together, but with the Islanders desperate to win a series for the first time since 1993, time isn’t exactly on their side. They return to Florida for Game 5 Friday, and though he reunited the original fourth line in the third period, there’s no guarantee that it’s going to stay that way. Especially not with the Islanders struggling to find offense early in the game — they’ve been behind every game this series, no matter how many times the team has stressed the importance of quick starts.

“We’ve got one line — 91, 51, 21 — creating all our offense right now and we have to find a way, like we did in Florida [in Game 1] where we had secondary scoring,” Capuano said. “If not, it’s going to be tough.”

The truth is, he said, he liked what he saw when he moved his fourth line around in the second period, and matchups would dictate whether he’d do it again.

“I thought the other lines, we got going a little bit,” he said. “We generated. In the third period, we put them back together just to see if we could reignite some magic with those guys but everybody goes through a little bit of a tough stretch. Those guys have been there all year for us so now we go back on the road and now decisions will be made.”