Eddie Chambers vs. Tony Thompson off

Heavyweight contender Eddie Chambers said he is suffering from a bad back and has withdrawn from his title elimination bout against Tony Thompson, which was scheduled for Oct. 28.

Chambers and Thompson, who are good friends, were supposed to meet at Bally's in Atlantic City, N.J., on Showtime's "ShoBox: The New Generation." A mandatory title shot at heavyweight champion Wladimir Klitschko -- who has already beaten both of them by knockout -- was to be at stake.

The show will go on, however.

Originally a tripleheader, the show will now feature two televised bouts, with super middleweight prospect Brandon Gonzales (14-0, 10 KOs) facing veteran Ossie Duran (26-8-2, 9 KOs), and 2008 U.S. Olympian Javier Molina (9-0, 4 KOs) against Artemio Reyes (13-1, 11 KOs) in an eight-round junior middleweight bout.

"It's always disappointing when you have a fight with a lot on the line and one of the fighters gets hurt. There's nothing you can do about it. It's part of the sport," Dan Goossen, who promotes Thompson and Chambers, told ESPN.com on Wednesday. "It's one of the breaks of the game. I just hate to see Tony Thompson putting all this hard work in and now he's faced with not fighting next Friday."

Chambers (36-2, 18 KOs) had been training in his hometown of Philadelphia but experienced tightness in his back.

"This has been an ongoing thing and it just caught up to me," Chambers told ESPN.com. "My back has always been tight and that's a very stubborn area in your body. But it's really gotten to me. I was sparring last week and it really got to me.

"I don't think it was any specific move or punch, but it became unbearable. I just don't want to get in there with a guy like Tony and half-ass it. You're asking for either a bad performance or a loss, and I don't want either of those. It's unfortunate. I worked really hard, but I'm injured."

Chambers said he had X-rays and would have an MRI exam to get to the bottom of the problem.

"In camp, my back was tight," he said. "I would do some rounds and then I couldn't move. I was going to tough it out, but I just couldn't perform. My back was tightening up when I was just walking around."

Thompson (36-2, 24 KOs), who turned 40 on Tuesday, and Chambers, 29, both were the two fighters remaining in an IBF-sanctioned four-man tournament to produce Klitschko's next mandatory challenger.

Goossen said he is in contact with the organization to figure out what to do next. The organization could go down its rankings and mandate that Thompson face the next available contender.

"If we can't reschedule the fight, I believe Tony should just become the mandatory because he has performed within the guidelines of the tournament," Goossen said. "Or we can try to reschedule the fight for later in the year."

Chambers and Thompson both suffered late knockouts in previous mandatory title shots against Klitschko. In July 2008, Klitschko stopped Thompson in the 11th round of what was, to this point, his most competitive defense. In March 2010, Klitschko dominated Chambers from start to finish before knocking him out cold with five seconds left in the 12th and final round.

Dan Rafael is the senior boxing writer for ESPN.com. Follow him on Twitter @danrafaelespn.