Something isn't kosher in the Catskills. Roberto Duran, who is scheduled to fight Sugar Ray Leonard in Montreal for the welterweight championships on June 20, left his training camp at Grossinger's Friday to consult physicians at New York City's Jewish Memorial Hospital for a sprained back.

Duran was examined by three or four physicians, according to Charles Gellman, director of the hospital. They included an orthopedist, an internist and a physical therapist who prescribed exercises Duren could do without hurting his back, and told him to take it easy for a few days.

Gellman said the injury is "nothing with nothing." Asked if there was any reason to think the fight would have to be postponed, Gellman said, "Not as far as we can tell at this point. We think the fight can go on. But no one has a contract with God. You don't know what will happen tomorrow."

"I just hope he doesn't aggravate it," he added.

Gellman said that Duran's trainers had him running up hills and that the muscles in his back and thighs had tightened. "Then he threw a punch when he was sparring and threw it very hard and more or less sprained his back," Gellman said.

Dr. Keith Holder, Duran's friend and a neurosurgeon in Panama, recommended that Duran see a doctor when he arrived at the training camp on Thursday. Reached at Grossinger's yesterday, Holder said, "It's like when you're walking around and you twist your ankle. It's very sinmple usually it subsides in 24 hours."

Asked how Duran was feeling, Holder said, "He ran very well this morning. Now he's playing dominoes. He's happy as a bell."

Duran's manager, Carlos Eleta, denied that Duran had received any treatment. He said, "Someone had gotten the wrong story. I passed by the hospital to visit a friend with a stomach ache."

Gellman said he expected Duran to be back in full training by Monday. "He's got to, he said. "He's got to bring some weight down. Right now, he's 153-154."

Dave Jacobs, Leonard's trainer said "I'll have to see it to believe it. I'm pretty sure they'll try anything to throw you off but there's no way they'll throw us off.

"If he did hurt his back, I hope it's not bad and that he gets back into training. When you start to fool with a back, it's not kosher. If there is something wrong with it, it's an indication, they can come up with an alibi."

Leonard took the weekend off from training.