A promising young boxer getting ready for an upcoming fight nearly lost consciousness on Monday in his working-class neighborhood due to the high temperatures pummeling the city after training in Brooklyn.

John Duddy, an undefeated middleweight from Queens who is 17-0 with 15 knockouts, was scaling the steps of his elevated first-floor apartment in Middle Village clutching a heavy gym bag when a case of vertigo brought on by the harsh temperatures caused him to nearly faint.

Luckily, his manager, Tony McLoughlin, was there to prop him up and guide him to his apartment. McLoughlin switched on the air conditioning and phoned Duddy’s promoter and trainer.

Duddy, 27, is one of the most popular fighters in the sport. He was born in County Derry, Ireland and draws largely from his roots to attract big, lively crowds.

He had been training at Gleason’s Gym for a fight on August 10 in Las Vegas against Carlos Bojorquez, but Duddy’s team agreed to cancel the fight after they spoke with Dr. Osric King, a ringside physician from New York, Jim Borzell, an advisor to Duddy said in a phone interview yesterday.

Dr. King identified the illness over the phone to Borzell as heat prostration, which is brought on by excessive exposure to high temperatures and a loss of fluids. Duddy, who didn’t return phone calls, had appeared lackadaisical and careless in training recently.

“He’s been flat for a while now,” said his trainer Harry Keitt, who cut short a sparring session Monday because Duddy was taking too many punches. “He’s just been going through the motions with his hands dropping. He’s sparring and getting hit with stupid stuff. He’s been getting hit by guys who don’t have any business being in the ring with him. Nothing is right for this fight. Mentally, he wants to convince himself to take the fight, but I know what I’m looking at, and I’m not looking at the same John Duddy that I know. He’s from Ireland. He’s not used to this heat.”   

The decision to call off the bout was complicated by Duddy’s immense popularity. He had already sold 200 tickets for the August 10 show to fans from as far away as Ireland and San Francisco, Borzell said.

Duddy was scheduled to drum up publicity for the August 10 bout with an appearance at the Mohegan Sun last week, but he cancelled, complaining of fatigue.

An amateur fighter, bothered by the heat, passed out while sparring earlier this week at Gleason’s, Keitt said. Bruce Silverglade, the owner of Gleason’s, couldn’t recall the incident, but said that most fighters were working out in the mornings and evenings instead of the afternoon sessions when the heat is oppressive.

Duddy is scheduled to fight on September 29 at Madison Square Garden against the former junior middleweight champion Yory Boy Campas, who is Mexican, in a show appropriately titled “Shamrocks and Sombreros.”