Former lightweight champ Joel Casamayor, suffering from a sprained lower back, withdrew Wednesday from his April 4 fight against former titlist Julio Diaz.
"He's not going to be able to fight," manager Luis DeCubas Jr. told ESPN.com. "He has a lumbar spine sprain."
It's the second injury to knock out one of the participants on Golden Boy Promotions' four-bout "Lightweight Lightning" pay-per-view card, which will take place at the Frank Erwin Center in Austin, Texas. Former junior lightweight titlist Jorge Barrios dropped out a few days ago because of a broken jaw.
DeCubas said Casamayor's back has been bothering him for more than a week.
"He's laid off sparring for a while. His back is real tight," DeCubas said. "He hasn't sparred for about a week and a half. Joel was right on track, but sometimes your body just says no."
DeCubas said Casamayor tried to rest but his back was still giving him problems and his doctor recommended that he lay off for about a month.
"He should be fine but the doctor said there was no way he could fight April 4," DeCubas said. "He was not even 75 percent. It's terrible. This was the perfect fight. Julio Diaz is a hard guy to fight but if we beat a guy like Julio Diaz, it puts us right back in [the title picture]. We're very disappointed. Joel was sparring one day and he felt something and stopped. I thought maybe he was just a little rusty or it was something he just needed to rest for a few days. But it didn't get better. Joel is not the kind of guy who pulls out of fights, but if you can't go, you can't go."
Casamayor (36-4-1, 22 KOs), 37, was looking to rebound from his last fight in September, when Juan Manuel Marquez knocked him out in the 11th round to claim the lineal 135-pound championship.
Golden Boy Promotions matchmaker Eric Gomez told ESPN.com he was looking for a replacement to face Diaz (36-4, 26 KOs).
Diaz, 29, has won two in a row since being stopped in the ninth round by Juan Diaz in a unification fight in October 2007. But Diaz's wins had come against lower-level opposition, so he was looking at the fight with Casamayor as way to springboard into an even bigger fight.
Barrios' broken jaw opened an opportunity for 2004 U.S. Olympian Vicente Escobedo (19-1, 12 KOs), a Golden Boy prospect who is stepping in for Barrios to face former title-holder Carlos Hernandez (43-7-1, 24 KOs), 38, on the card.
"When I was asked to step in for Barrios against Carlos Hernandez, I didn't hesitate to say yes," said Escobedo, 27, who originally was slated to face Kevin Kelley on April 30 in Sacramento, Calif., in an untelevised bout. "This is an amazing opportunity for me and while I have a lot of respect for Carlos, I know that beating him will be a huge step in my career."
Said Hernandez, "Vicente Escobedo is a good young fighter with a lot of talent and potential, but he will not prevent me from achieving my goals. On April 4 my experience and hunger will be the difference in this fight."
In the main event, former junior lightweight title-holder Edwin Valero is moving up to lightweight to face Antonio Pitalua for the world title recently vacated by Manny Pacquiao and Michael Katsidis fights Austin's Jesus Chavez.
Dan Rafael is the boxing writer for ESPN.com.