PEORIA, Ariz. -- He can move almost seamlessly from clubhouse to bullpen, unnoticed by those who are busying doing the same. This suits Mark Prior perfectly fine. He's on the backburner, more or less, here in camp as a non-roster invitee, trying to get healthy without facing a barrage of daily inquiries as to how close he is.

The fact of the matter is, Prior has no idea how close he is or might be to climbing back on a Major League mound, something he hasn't done since 2006, when he was with the Chicago Cubs. This isn't a frustrating endeavor anymore for him, the attempt to plot a return. The best timetable is no timetable at all.

"I'm 28 and no one knows what the future holds," Prior said. "If I can get back to 80 percent or 90 percent of what I used to be, then that's still pretty good. I look back to those three, four years in the big leagues and I pitched pretty well and did the things I had to do to help us win games. I don't know if those memories haunt me, but they motivate me."

This is why Prior is essentially on his own throwing program here in Peoria when other pitchers follow a strict bullpen program and stints in Cactus League games, which start today here in the desert and continue through April 2.

Prior is trying to return to the Major Leagues following two significant surgeries to his right shoulder, the first in 2007 by renowned orthopedic surgeon Dr. James Andrews to repair a 180-degree tear of his labrum as well as a split of the shoulder capsule.

Then, on the heels of a year-long recovery and rehabilitation program, Prior suffered a serious setback when he tore the anterior capsule in his shoulder, a gruesome injury of sorts that saw the capsule tear away from the humerus bone. He had surgery last June.

Doctors informed Prior that such injuries were not only uncommon among pitchers, but went as far to add that this particular injury is "often associated with traumatic events ... typically from a fall."

Traumatic events? It all happened on one innocuous pitch.

"Last year, I felt like I was making some progress," Prior said. "I was throwing a bullpen and with one pitch ... one pitch and it hurt [really bad].

"I think that one shocked us all. That was hard, because you feel like you are getting close and that the team is probably looking for you to give them a second-half jolt. That caught everyone off-guard."

That surgery was more devastating to Prior than the one he had in 2007, because he felt as if he was getting close to returning. Looking back, Prior feels further along now than he did a year ago. It leads him to believe he's making progress. Pain-free bullpens are something for him to get excited about.

"I think we all feel for Mark and what he's had to go through," Padres pitcher Jake Peavy said. "You've got to commend him for the valiant effort he's put in. For him to have multiple surgeries and endless rehab ... that's got to get old.

"That's why, as a baseball fan, you want to see a guy like that succeed. It would be great for him to come back and do what he once did."

The pain-free feeling in Prior's shoulder and the progress he's making has been enough to keep the right-hander plugging away, enough to keep him from entertaining the one thought that he's mostly been able to avoid, even in the darkest of times -- retirement.

"I won't say I haven't thought about it," Prior said. "But they were usually the thoughts I had after a surgery. The first surgery [2007], it was more, 'Thank God, I have answers.' It was more of a relief, even though I knew it was going to be an uphill climb to get back."

He had no idea. Prior gets further and further from that 18-6 season he had in Chicago in 2003, when he had a 2.43 ERA with 245 strikeouts while pitching magnificently down the stretch as the Cubs landed in the postseason.

Prior's time away from the mound has been filled with countless hours of rehabilitation and plenty of second-guessing by pundits who have tried to associate Prior's run of injuries with what is perceived a poor mechanics.

"In the age we're in, there's always those Monday-morning quarterbacks," Prior said. "But I was a workhorse in college, a workhouse my first few years in the big leagues. I never really had anyone question what I did and how I did it. In fact, it was probably to the extreme the other way, where I was trying to rope them back in. These people are telling me everything looks so smooth. I was like 'I'm nowhere near perfect.' ... I have a lot of things I was always working on.'"

San Diego manager Bud Black said this week that he "doesn't have any problems" with Prior's mechanics. To this day, Prior hasn't had anyone comes up and tell him what he should be doing differently.

"One of my philosophies on pitching is everyone does it different," Prior said. "I don't do it the same way Jake [Peavy] does it and Jake doesn't do it the same way [Chris Young] does it.

"It wasn't until the injuries that people started to question that. The funny thing is I have never had a pitching coach tell me I had to make a drastic change or that I was going to have problems. No one has ever approached me about it."

Which is why Prior looks very much the same pitcher, if you watch him throw a session in the bullpen in Peoria, Ariz., like he did while playing at USC or with the Cubs, when he was regarded as one of baseball's true up-and-coming talents.

Today, he moves without fanfare from drill to drill, biding his time until his body deems itself ready for another challenge, whether that be pitching to live hitters or advancing to pitching in Cactus League games.

When will Prior be ready? His body will let him know.

"The door hasn't been closed on me," Prior said. "And until someone tells me I don't have a job or a spot, I'm going to keep going. I want to go out on my terms. And until my body tells me that it's not going to work, I'm going to make every effort to make this work."