Florida’s Sam Bennett checks Boston’s Brad Marchand in the first period of Game 3 of their second-round playoff series on Friday in Boston. Michael Dwyer/Associated Press

Brad Marchand spent his 36th birthday off the ice. The Bruins captain, who was injured in the Bruins’ 6-2 loss to the Panthers on Friday, missed practice on Saturday.

“He’s upper body, day-to-day,” Jim Montgomery said.

The Panthers lead the best-of-seven second-round playoff series, 2-1. Game 4 is at 6:30 p.m. Sunday in Boston.

Marchand appeared to suffer an injury on a hit followed by a punch from Florida’s Sam Bennett in the second period. Florida Coach Paul Maurice didn’t see anything illegal.

“No, and I don’t think most of you would, either. It was just a collision,” he said. “In a perfect world, every team has everybody healthy. Nobody likes to see anybody hurt.”

Montgomery tried to make his point without crossing a line.

“There’s a history there with Bennett. Good hard player,” he said. “But there’s clearly evidence of what went on. People can say it’s not intentional. We have our view of it.”

Marchand returned to the ice initially but didn’t come back for the third period.

Marchand doesn’t need to practice to play. He has missed a handful of practices for maintenance this season, only to play in the game. He’s made it clear that if he can play through something, he will.

Montgomery shuffled his lines at practice so no one player specifically replaced Marchand. Danton Heinen, who has been out, looks ready to step back into the lineup.

Marchand has three goals and seven assists in nine playoff games. He had 29 goals and 38 assists in the regular season. He’s a regular on the top power-play and penalty-killing units.

Montgomery thought the Bruins played better after Marchand’s injury, trying to make up for his absence in the third period.

“I thought we rallied because of our captain,” Montgomery said. “I thought (David Pastrnak) and Charlie McAvoy did a great job with him not being on our bench, and I thought our players started competing like Brad Marchand would.”

MONTGOMERY DIDN’T KNOW exactly why his team started slowly again in Game 3, but he blamed himself.

After the Bruins’ 6-2 loss, Montgomery answered almost every question by blaming himself.

“We have to get better. I have to give the players a better plan,” he said. “Florida was significantly better than us. I have to come up with a better game plan.

“We weren’t very good for the first two periods. I don’t think we were on top of our game,” he added. “The last two periods of last game and the first two periods of tonight, it’s not been good enough. That’s why I said it was my fault. We have to do better.”

Why did it take so long for his players to find some energy?

“I don’t know. It’s not good enough. Florida was good enough,” he said. “We weren’t. Move on to the next game.”

Asked to clarify something he said:

“We didn’t play well enough, that’s why I take responsibility.”

Montgomery wasn’t sure if changes were coming to his lineup or not, but said the start of fixing things was simple.

“Get a good night sleep. Come to the rink tomorrow and get better,” he said.