The Phillies said they thought his knee caused those struggles, so they met Tuesday and decided to put him on the DL.
"It was time to go ahead and make the decision for him," Amaro said. "His slider was not as sharp. His fastball did not have the velocity. He's not able to drive off the back leg. You could see he was doing some things mechanically that was of concern."
Ryan Madson is the closer in Lidge's absence.
J.C. Romero is the setup man, although Phillies manager Charlie Manuel said Phillies right-handers Chad Durbin, Clay Condrey and Chan Ho Park could slide into that role depending on the team and situation on a given night.
Lidge, who couldn't be reached for comment, returned to Philadelphia on Tuesday to see team physician Michael Ciccotti after Phillies officials told him of their decision.
Ciccotti determined that Lidge did not need his third MRI examination since late April, although he gave him his second anti-inflammatory injection. Ciccotti also said while Lidge has an inflammation in the knee joint, there are no signs of structural damage. In fact, Ciccotti said the knee has improved.
Lidge is expected to begin a rehab process beginning Wednesday in New York.
"We do not think that there is anything structurally wrong with him," Amaro said before Ciccotti's exam. "[In the previous MRIs] he had some inflammation and some fluid."
Lidge has had problems with his right knee since he joined the Phillies in a Nov. 2007 trade with the Houston Astros. He had surgery on the knee during Spring Training 2008. He received a cortisone injection in the same knee this April because of inflammation.
But the inflammation never went away.
Phillies pitching coach Rich Dubee said Lidge expressed concerns recently that the knee had not improved.
But Lidge pitched through it and the Phillies said he would have continued to pitch through it. That is why the organization said they made the decision without him.
"Brad wasn't going to say he wasn't healthy," Dubee said. "He doesn't want the ball taken out of his hand. This guy is a tremendous competitor, and he wants to be in the back end of games. We basically took it out of his hands. He didn't give the ball up. Believe me."
"I'm sure he's not pleased with the decision," Amaro said. "He wants to pitch and help the team. But I think he's also realistic enough to know that we need him for the long haul."
The Phillies are hoping Lidge only needs a couple weeks before he is ready to return, but he might be out longer depending on what Ciccotti finds Tuesday. Because he has not pitched since Saturday in Los Angeles, Lidge is eligible to be activated June 23.
"We will bring him back when he's 100 percent," Dubee said. "We don't want to bring him back beforehand. Again, we want him being able to pitch with no other concerns on his mind except executing his pitches. Hopefully it won't take too long, but who knows?
"We're talking long term here. If this guy continues to pitch with this thing we don't know what kind of damage he's going to do to the rest of his body or his knee or whatever. And then we lose him for the rest of the season. We thought it was a great time right now to make sure we get this thing taken care of so that we do have him over the long haul."
Interestingly, Dubee said Sunday night on ESPN that he thought Lidge's confidence -- and not health -- was the primary reason for his struggles.
"How much do you want people to know about an injury?" Dubee explained. "Do you want the opposition to know he's not moving really well with his knee? Sometimes you don't tell the whole story. I don't want people to know he can't bounce around the mound very well because then you'll see four guys come up there and bunt in a row.
"He told me it wasn't right and that there was concern of what is going on and why it hasn't improved. Some days it felt pretty good. Other days it felt pretty bad. He was honest enough to say it wasn't right."
Lidge gets his job back upon his return, regardless of how well Madson performs in the role.
"Brad Lidge is our closer," Amaro said. "He's done nothing to lose his job."
"I view Lidge as our closer, but at the same time we'll see how Madson does," Manuel said. "But at the same time, Lidge is our closer. We signed him for three years to be our closer. Right now he's still our closer."
They just hope he can pitch like he pitched in 2008, when he went 48-for-48 in save opportunities, including the postseason.
The Phillies purchased catcher Paul Bako's contract to take Lidge's place on the 25-man roster, which allows Manuel to use Chris Coste as a pinch-hitter. The Phillies could have recalled outfielder John Mayberry Jr., but they said they want him to play every day in Triple-A Lehigh Valley.
"All things considered, I think Coste is probably better suited for that role," Amaro said.