Perhaps the worst news for the Ottawa Senators about their not-so-excellent New York adventure this week is that they now have to come back — for Game 6 on Tuesday night.

That does not bode well for a team that in two games at Madison Square Garden lost to the Rangers by matching 4-1 scores — and might have lost their captain and best player, all-world defenseman Erik Karlsson.

“I don’t even know what to say; we just have to be better all around,” current Senator and former Ranger Derick Brassard said after Thursday night’s 4-1 loss dropped Ottawa into a 2-2 series tie in the Eastern Conference semifinal.

Then he added a hopeful note, sort of, saying, “Maybe it’s a good thing for our team to get a couple of slaps in the face and kind of wake up a little bit.”

Indeed, the Senators seemed to sleepwalk through the games in New York, but there is more to their problems than lack of energy.

They already had been operating with a less-than-full-strength Karlsson, who began the series with two hairline fractures in his left heel.

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Then things got worse in the second period. He fell awkwardly over sliding Ranger Chris Kreider, came up wincing and was nowhere to be seen when his teammates returned from the second intermission.

Coach Guy Boucher said after the game that Karlsson had a lower-body injury and that he could have returned to the game if necessary.

But might he have to miss Game 5 in suburban Ottawa on Saturday? “Not right now,” Boucher said.

Said forward Kyle Turris, “We have to find a way to do it if Karl’s not back.”

The Senators entered the series sporting a 1-3-1 neutral- zone trap that has flummoxed many opponents. Now it appears they are the ones who are flummoxed.

“They made adjustments to our system and they’re making plays and they’re getting through it right now,” said goaltender Craig Anderson, who was pulled after two periods with the score 3-0. (Boucher said Anderson will start tomorrow.)

The Senators kept talking after the game about how both teams held serve at home, but while the Rangers left Canada after Game 2 feeling pretty good about how they had played despite losing the first two games, the same cannot be said of the Senators as they leave the United States to return home.

Said Brassard, “We didn’t really have a pushback. We were just chasing the whole time . . . We have to remind ourselves that we can make plays.”