Cruiserweight titlist Guillermo Jones suffered a back injury when he tripped getting out of the ring after a training session, forcing him to withdraw from Saturday's title defense against Ryan Coyne.

"I'm absolutely dejected, I am still," Coyne told ESPN.com from his training camp in Colorado Springs, Colo., on Saturday night. "I was in shock when I heard. I couldn't believe it. I trained hard, I left my family behind, and I've been living under a rock and giving it my heart and soul for eight weeks, and it's not going to come to fruition."

The fight was due to take place at the Family Arena in the St. Louis suburb of St. Charles, Mo., Coyne's hometown, on the untelevised undercard of an HBO tripleheader.

Former junior welterweight titlist Devon Alexander (21-1, 13 KOs) of St. Louis -- in his first bout since losing his belt to Timothy Bradley Jr. in a January unification match -- headlines the card against big puncher Lucas Matthysse (28-1, 26 KOs) of Argentina.

With Jones out, Coyne (16-0, 6 KOs), known as "The Irish Outlaw," will face late substitute David McNemar (13-0, 10 KOs), 38, of Parkersburg, W.Va.

"I'll get a title shot. I just have to stay positive," Coyne said. "I'll still be in business on Saturday night and I'll get a win and keep pressing forward."

Jones was training at promoter Don King's facility in Orwell, Ohio, and when he stepped out of the ring after a training session on Thursday, he slipped on the top step and fell to the ground, suffering a back injury, King spokesman Alan Hopper told ESPN.com.

"The doctor looked at him and said, 'You need to rest, you can't train. You're hurt,' " Hopper said. "At first they thought it might be cracked ribs, but it was a back injury that radiated to his side. Naturally, the hope is (Coyne) can get by (McNemar) and Guillermo can get healthy and they can fight when he's ready. But for now, Guillermo has been ordered to bed rest."

Coyne, 28, a former participant on "The Contender" reality series and former University of Missouri football player, was looking forward to fighting for a world title in his hometown.

"I wanted to fight for a world title in my backyard, but it was almost too perfect," said Coyne, who grew up four miles from the Family Arena. "So it's incredibly disappointing, but I've got a job to do. I'm gonna get my shot eventually. I've got great fans and I'm not going to let them down."

McNemar is not even close to the level of Jones (37-3-2, 29 KOs), 39, of Panama, a longtime top contender who finally won a title in 2008 and was due to make his second defense against Coyne, who would have been taking a significant step up in competition. McNemar has fought only once previously outside of West Virginia and has not had a fight since November 2007.

"He's a tough guy and he'll come to win and fight with heart, but he's not in our class," Coyne said. "He's going to get the wrath. I was prepared to take on a world champion, and I'm ready to rock 'n' roll. I'll look for the positive in the situation. I'm not happy. I spent eight weeks running mountains, but sometimes you get thrown an off-speed pitch and you just have to go with it and hit it to the opposite field, and then come up the next inning and hit the home run."