Robert Guerrero out four months

Former two-time titleholder Robert Guerrero will undergo arthroscopic surgery to repair his damaged left shoulder on Tuesday and won't be able to punch for about four months.

Guerrero suffered the injury sparring last Wednesday, forcing him to withdraw from a junior welterweight title bout against Marcos Maidana that was scheduled to headline an HBO card Saturday night at the HP Pavilion in San Jose, Calif., near Guerrero's hometown of Gilroy.

With Guerrero the star attraction and there not enough time to line up a top opponent for Maidana to defend his belt against, Golden Boy Promotions and HBO canceled the card last week.

Guerrero had been diagnosed with a partial tear in his left rotator cuff shortly after the injury, but after a follow-up exam on Wednesday with specialist Dr. Michael Dillingham, the San Francisco 49ers team physician, in Redwood City, Calif., he took the doctor's recommendation of surgery rather than rehabilitation.

"I'm just staying positive and praying about it," Guerrero told ESPN.com on Wednesday. "Right when I felt it, I thought, 'This isn't good.' And then waking up the next day and not being about to move my arm at all, it was scary. I was doing 500 push-ups a day and about 100, 120 pull-ups, and then you can't even move your arm. So it was scary.

"But I feel good about the test results and look forward to getting the surgery out of the way and getting my shoulder cleaned up and doing what I have to do to get back. I just got to take it one day a time, get the surgery done, get the rehab and get back to full-blown training."

Guerrero (29-1-1, 18 KOs) won titles at featherweight and junior lightweight and claimed interim belts at lightweight in April, but he was going to move up to junior welterweight to challenge Maidana for his belt. Now that is on hold.

"He'll spend two to four weeks in a sling and then can shadow box and jump rope and that sort of thing, but the doctor said he couldn't punch on it for three or four months," manager Bob Santos said. "So you're looking at probably four months before he can train 100 percent. Best-case scenario is if he is back punching on it in four months and then does a six- or eight-week training camp, you're talking about him being able to fight again in maybe February, March, April."

Guerrero, who is in a sling, tried to look on the bright side -- that with his left hand useless for the time being, he could focus on strengthening his right hand.

"I feel helpless walking around with a sling on, especially on my dominant hand, the left hand," Guerrero said. "I guess I got to look at the bright side. I can work on my right hand more and make it more effective in the ring. When you work with both hands, you're more of a well-rounded fighter. I throw (the right) but there is always room for improvement. But the main focus is getting the surgery done and getting it all cleaned up and getting back to 100 percent."

The injury happened during a sparring session last Wednesday at Guerrero's Big Bear, Calif., training camp. Guerrero, 28, was told that the injury probably stemmed from an injury he suffered many years ago when he played running back as a football player when he was 13 or 14. Guerrero said he remembered being tripped by the safety and crashing hard on his shoulder.

"The doctor said the arm looked fantastic except in the area where it was injured, that it had scar tissue," Santos said. "That is probably from having an initial tear in the rotator cuff back then. So the thought is that, over time, it finally tore again."

Guerrero had another problem with the same shoulder once as an amateur fighter that caused him to be sidelined for more than six months. A torn rotator cuff was not formally diagnosed either time because Guerrero did not have medical insurance to cover getting it checked out.

"We knew we weren't going to the doctor and we were taught that if you're hurt you block it out because you know you're not going to the doctor," Guerrero said. "If you can move it, it ain't broke. That's how we were brought up."

Guerrero had two MRIs to diagnose the tear and rehabilitation was an option, Santos said.

"Sometimes you can do rehab, but this being the second time, we thought it was best to get it fixed because this is how he makes his living, using his arm," Santos said. "So Dr. Dillingham said he would fix the problem and also be able to see what else, if anything, was going on in the shoulder that might not have shown up on the MRI.

"It's really a shame this happened because I have never seen him in such great shape. We took Maidana more seriously than any fighter we have ever faced. Unfortunately, that old injury reared its head and derailed us."

Although Guerrero is disappointed about losing out on the biggest fight of his career, Santos said there was also relief in receiving a diagnosis, and that it was not a career-ending injury.

"Robert told me, 'The more I kept thinking about it, every once in a while I would get a deep pain in (the shoulder) for the last few years,'" Santos said. "Now he knows something will be done about it. He would just say before when he felt it that he was the kind of guy who would suck it up and push through it, although this was different. I see him as relieved."

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