NEW YORK - Athletic performance is the sum of several interdependent parts, a complicated equation that combines health, ability and confidence to render the day-to-day production by which a player is judged. A diminished amount of any of the three can hinder not only the other two parts, but the sum of them as well.

So when the Phillies announced yesterday that they were placing Brad Lidge on the disabled list with a knee injury that has hampered him throughout the season, they did it with the hope that some down time and rehabilitation will restore both their star closer's health, and the overall production upon which they leaned during last year's World Series run.

A timetable for recovery has not yet been set, but a visit to team doctor Michael Ciccotti yesterday in Philadelphia eliminated any concern of a structural problem. Lidge, who received a cortisone injection after being examined, will be at Citi Field today, at which point he will begin a rehab program.

"He's had a couple MRIs on the knee, but we felt like it got to the point where it was affecting how he was pitching," general manager Ruben Amaro Jr. said. "Just like any other injury, if you have a problem in one area, you may overcompensate and put him in a position to have it affect some other part of his body - his hip, his back, his arm, something like that. And I just think for our peace of mind, for his peace of mind, I though it was important for him."

Lidge, who is 0-3 with a 7.27 ERA, said last night he would address reporters today at Citi Field. Amaro said that the closer was initially unhappy about the decision, but that both sides finished the day on the same page.

Lidge, who had two arthroscopic surgeries on the same knee last offseason, was sidelined from April 26 through May 2 after the inflammation first appeared.

In an interview with the Daily News on Thursday, Lidge said that the inflammation was still present, but that he did not think it had affected his performance.

"[The inflammation is] still there, and it might be for a while, but I'm not thinking about it when I'm pitching," Lidge said then.

The Phillies felt differently.

At the time, he had saved five consecutive games - including four on consecutive days - while allowing no runs and one hit in 4 2/3 innings. But over the weekend he twice surrendered one-run ninth-inning leads against the Dodgers, notching his fifth and sixth blown saves of the season. On Saturday, he allowed a solo home run to Rafael Furcal on a slider that did not appear to have its usual sharp break, a situation that pitching coach Rich Dubee said yesterday was more commonplace this season than last.

"He's throwing more of those this year than last year," Dubee said. "At times, his stuff has been probably better than last year. Just on a consistent basis it hasn't been there."

That doesn't jibe with public comments Dubee has made, including an interview Sunday on ESPN in which he said Lidge's problem had more to do with confidence then his health. Earlier in the year, Dubee said he felt Lidge's "stuff" was as good or better than it was in 2008, when he went 48-for-48 in save opportunities in the regular season and postseason. Then again, it doesn't make much sense for a pitching coach to question his closer's stuff when he is trying to instill confidence in him, and, Dubee said, it doesn't make sense to reveal details of a pitcher's injury.

"Sometimes you don't tell the whole story," Dubee said. "I don't want people to know that he can't bounce around the mound very well, because then you're going to see four guys go up there and bunt in a row."

The Phillies say that, in reality, they felt the reason for Lidge's performance was the inflammation in his right knee, which they think affected his push-off from the rubber, thereby diminishing the sharpness of his slider and the velocity on his fastball. At times, the stuff has been there. The difference has been consistency. After the Dodgers series, when they noticed a drop in his velocity - from an average of 94-96 mph to an average of 91-93, manager Charlie Manuel said - and a flattening of his slider, they decided that a trip to the disabled list was in order.

"Basically, what it boils down to, we thought the fact that the knee had something to do with his push-off, his drive, and also which way he goes and lands," Manuel said. "A lot of times, instead of throwing straight down right through the mitt, he kind of falls off to the left."

Amaro said that the decision was made strictly for medical reasons, and that Lidge would regain his role as closer once he returns. For the time being, righthander Ryan Madson, who entered last night having pitched 10 2/3 consecutive scoreless innings, will fill the void. Lefthander J.C. Romero, along with a combination of righties, will likely man the eighth.

"I view Lidge as the closer, but at the same time, we'll see how Madson does," Manuel said. "But Lidge is our closer. We signed him for 3 years to be our closer. Right now, he's still our closer."

The underlying reasoning was that, as long as Lidge is 100 percent healthy, he will be good enough to be the closer. When that point will occur remains to be seen.

"We're not going to put him back in a situation to play at this level of competition until he is absolutely physically 100 percent," Amaro said. "As I said before, it doesn't do us any good to have Brad Lidge at a certain percentage. Ninety-five or 90 percent doesn't do us any good, doesn't do our club any good to put him out there when he is not 100 percent." *

For more Phillies coverage and opinion, read David Murphy's blog, High Cheese, at http://go.philly.com/highcheese.