Frederic Weis of France might be surprised to learn that he’s not just joining the Knicks, but he’s also becoming a rebellious slave.

Maybe he won’t understand the term at first, so he’ll probably have to ask Larry Johnson to explain. It was Johnson who referred to the millionaire Knicks as “rebellious slaves” during the Finals.

But while they’re at it, the Knicks’ newest odd couple can also discuss their bad backs.

The 7-foot-2, 260-pound Weis, whom the Knicks selected with their first-round pick (15th overall) in Wednesday’s NBA draft, underwent back surgery on April 1 to trim his disc. No doubt, Weis is hoping his back doesn’t limit his game as it has Johnson’s.

Still, if Weis is healthy, he can be a very effective player, said NBA director of scouting Marty Blake.

“He’s the best center in Europe,” Blake said yesterday from his Atlanta office. “He’s an excellent shooter and can run the court.”

That’s ironic, considering Weis will be backing up Patrick Ewing, who can’t run the floor, and Chris Dudley, who can’t shoot.

After his surgery, Weis, 22, began playing on June 1, and is currently participating for France’s national team in the World Championships. He didn’t attend the NBA’s Pre-Draft Camp, however.

Weis averaged 13.4 points and 7.3 rebounds this past season for Limoges, a pro team in France. This was his fourth year with Limoges, but his first season in which he averaged double-figures in points. Blake said Weis, who prefers playing with his back to the basket, would have been taken quickly if the Knicks had not picked him.

“This guy can play,” Blake promised.