Jose Valentin tries not to think about it — that piece of his body that isn't really his, that once belonged to another human being, that's now fused to him forever.

Jose Valentin tries not to think about it — that piece of his body that isn't really his, that once belonged to another human being, that's now fused to him forever.

He doesn't know if the life-altering flexible strip of fibrous tissue came from a male or female, or even how old the person was, only that he or she was young enough to be in the prime of their life, somewhere probably in their 20s.

Which means that for something seemingly as trivial as Valentin getting another shot — and a long one, at that — at playing major-league baseball again, for yet another career comeback with the Mets, something sudden and tragic had to occur.

Someone had to die to put Valentin's right knee back together.

"Someone whose ligament," said the 38-year-old veteran, "was stronger and fresher than mine."

The surgery was done in late September: Instead of using a ligament from his own hamstring to replace his torn anterior cruciate ligament, Valentin opted, on his doctor's suggestion, to fix himself with one from a cadaver — a procedure that's becoming increasingly common, but, to the layman, no less mind-blowing.

Understandably, before agreeing to do it, Valentin had to wrap his head around the idea.

Because, at first, it totally freaked him out.

Sounded too strange, too wrong to him.

"But my doctor convinced me that this was the best way to make my knee better, and for the recovery time to be so much faster," Valentin said.

He waited a whole month for the right donor, one with the same blood type, one that his body wouldn't reject, and five months later, here he is in spring training, without the crutches that he limped around on for most of last season, for what he knows is likely his last go-around, his last comeback before he's forced to shut it down for good.

"It all depends on whether my knee responds," he said, "and whether the Mets or another team wants me."

For the moment, he's going slowly, his knee still too weak to do all the practice drills, to drive himself at full speed. He's also worried about ruining everything by reinjuring it, especially careful when he walks up stairs or suddenly changes direction.

"But I'm still very strong mentally," he said. "I'm still very positive. And I still feel deeply about the game. If everything goes right, if my body can hold on, I probably have a good couple of years left in me."

In 2006, his first year with the Mets and the season after shredding his knee with the Dodgers during a brutal-looking slide at home plate, Valentin made the unlikeliest of comebacks.

After playing so little at the beginning of the season he nearly asked out of Flushing, he ultimately emerged, despite wearing a knee brace, as the Mets' biggest surprise in the team's wonderful run for the NL East title, replacing the failed experiment of Kaz Matsui at second base and appearing to do something special, if not game-changing every day — a dazzling, diving stab up the middle to turn a big double play one day, a huge homer or some clutch hit in the gap the next.

He then followed that magical year with an utterly lost one, suffering two injuries to his right leg in 2007 — a fractured tibia, but more importantly a torn ACL — that made him miss all but 51 games.

He knows this comeback will be different than the last.

"This will be harder," he said. "This injury (to my ACL) is more serious than the knee injury I had before."

He understands that, at best, he'll likely start this year for the Mets' Triple-A club in New Orleans, and if he isn't promoted by May 1, he has the team's promise to release him, so he can pursue a major-league roster spot elsewhere.

"All I can do is keep trying," he said. "If it's the end, if the phone never rings for me, I'll go to Plan B and head back home to Puerto Rico, to Manati, and enjoy my family for awhile. Then maybe I'll try to get a coaching job in the minors."

In the meantime, as hard as he tries to forget about that piece of his body that came to him by way of a tragedy, from some vibrant 20-something soul he'll never know but who has given him a chance — even if it's an outside one — to keep doing what he loves, he can't help but let thoughts of that person occasionally trickle in and consume him.

"The tragedy of it," he said with a solemn tone, shaking his head before shifting his eyes to that reconstructed knee, staring at it without blinking.

"If I make it back," he added after a pause, his fingers now gently stroking the scar left from the surgery, "I owe that person a lot."