NBA

Knicks give Celtics plenty to ponder

TORONTO — There are enough worries about the Knicks to fill volumes of scouting report binders for the Celtics. There’s the size factor. There’s depth. There’s shooting. Even apparent weaknesses are a concern: Suddenly, “old” becomes “experienced.”

But Celtics coach Doc Rivers said he gets the biggest headache when he simply thinks of the Knicks offense.

“They’re really good offensively. They really are. They spread the floor and they do a terrific job,” said Rivers, whose Celtics lost their regular-season finale, 114-90, to the Raptors Wednesday night before seeing the Knicks in the playoffs starting Saturday at 3 p.m.

And the biggest pain in the pants wrapped in the biggest headache surrounded by the biggest trouble for Boston is NBA scoring champ Carmelo Anthony.

“Melo has had an MVP season. Obviously, LeBron is the MVP but Melo has had an MVP-type season,” said Rivers, who with his coaching staff wore Boston Marathon pins to honor the victims of the bombings while Celtic players wore black patches with a moment of silence observed before the game. “He’s really changed as a player. He gives the ball up, he moves, he cuts. He’s been terrific.”

But remember, it’s the whole Knicks team, the Atlantic Division champ, the East’s No. 2 seed that provides Celtic heartburn.

“It’s all the other guys [like] J.R. Smith,” Rivers said. “They have a lot of veterans going into the playoffs. That’s obviously a concern. Veterans show very well in the playoffs. Something we usually have the upper hand on, they do.”

The other chief tasks awaiting Boston?

“Defending the three and rebounding,” said swingman Terrence Williams.

“We have to work our transition defense matching up with them because they have a lot of guys who can stretch the floor and shoot the three,” said guard Courtney Lee, who said stopping the threes is “tricky” at best.

“Because I’ve seen rotations where they have Carmelo at the five. When you have a big out there it’s confusing for him, because bigs are taught to run back and protect the paint. You can’t do that with Carmelo at the five,” Lee explained.

It just always seems to come back to Anthony.

“He can score at will,” said Jeff Green, who played all 81 games this season after sitting all of 2011-12 following heart surgery.

There is the theory of let Anthony get his and shut down everyone else. Rivers adheres to that thinking — to a point.

“Any team, if you let the best player get his and stop everyone else … but you can’t let the player get his shooting 55 percent. If the best player gets his shooting 35 percent, then you’re good,” Rivers said. “But you can’t let a great player be efficient and think you’re going to win. I’ve never subscribed to that theory.”

The Knicks beat the Celtics three of four games this season, losing the Anthony-Kevin Garnett “Honey Nut Cheerios” game at the Garden Jan. 7. In that game, Anthony shot a wretched 6-of-26. But the Celts attacked everyone.

“We put a lot of full-court pressure on the guards and we threw the first punch,” Lee said.

In light of the Boston Marathon tragedy, Rivers noted there will be a renewed respect and admiration as human beings when the storied franchises go at it again — but the rivalry stays intact. And Rivers has been moved by the support for Boston other cities have shown.

“Awesome. 9/11 was very similar. You saw the Yankees-Red Sox hats,” Rivers said. “Don’t get me wrong, we still hate each other in sports. But not in life. You can separate the two things. All the big cities do a great job of showing that we’re with you and we’re against you. It’s a neat little thing.”

fred.kerber@nypost.com