A MRI exam revealed Moyer, who left Tuesday's game after one inning, has a sprained ulnar collateral ligament and a strained flexor pronator muscle. But Amaro said it sounds like the injury is more severe than the elbow problem J.A. Happ suffered earlier this season.
Happ has not pitched for the Phillies since April.
"He is out indefinitely," Amaro said of Moyer. "If he has surgery or a regular conservative rehab, he's going to be out quite some time."
The Phillies remain in serious contention to acquire Astros right-hander Roy Oswalt before the July 31 non-waiver Trade Deadline, but sources indicated any deal for any player is unlikely to happen before the weekend. Perhaps that is why Amaro announced after the Phillies' 2-0 victory over the Cardinals at Busch Stadium that Kendrick and Happ will fill holes in the rotation Saturday and Sunday against the Rockies at Citizens Bank Park.
Amaro needed to find two starters instead of one because Moyer could be finished for the season.
Amaro said Moyer, who will be placed on the disabled list Saturday, will have one more exam before they determine whether or not he needs surgery.
It is a blow to a team that has made it clear it needs pitching help.
Moyer went 9-9 with a 4.84 ERA in 19 starts, which Amaro called a pleasant surprise after being pulled from the rotation last season for Pedro Martinez and having three surgeries in the offseason to repair multiple abdomen tears, a blood infection and a balky knee.
Moyer became the oldest pitcher in baseball history to throw a shutout at 47 years, 170 days old, when he blanked the Braves on two hits on May 7. He went 6-5 with a 3.48 ERA in an 11-start stretch from May 7-June 2 before struggling in the two starts preceding his final start Tuesday.
"It's tough. He's a mentor to all of us," Phillies left-hander Cole Hamels said. "There's always something you can learn from him when he's pitching. He's a good balance on our pitching staff. The speed differential can really screw up an opposing team."
"He's been a lot of ways a godsend for us," Amaro said. "Yeah, he'll hurt our rotation, but with one door closed, hopefully another one opens up."
Amaro has said for weeks the Phillies need starting pitching. Asked if Moyer's injury made it more imperative he acquire somebody in a trade, he said, "I'm not going to get into that."
Asked if he had any irons in the fire, he said, "I'm not going to get into that."
There is some thought if the Phillies fall too far from contention, they could back away from Oswalt or D-backs right-hander Dan Haren, who they also are interested in, and save their prospects. But Oswalt and Haren are in the middle of multi-year deals, so the Phillies still could make a trade knowing they will have either pitcher beyond 2010.
Oswalt is owed roughly half his $15 million salary this season and $16 million next season. He also has a $16 million club option in 2012, which ESPN.com reported Oswalt would insist be exercised before he accepts a trade.
Oswalt (6-11, 3.12 ERA) has the right to veto any trade.
Haren (7-8, 4.60 ERA) is owed roughly half his $8.25 million salary this season, $12.75 million in 2011 and 2012, and has a $15.5 million club option with a $3.5 million buyout in '13.
It appears Oswalt remains the Phillies' primary target.
Asked if he expects the Phils to make a trade for a pitcher, Hamels said, "I don't know. I go out there and do my job and that's all I can really affect. I was making a joke about it the other day -- where were all the starters on the bench, because it was just Roy [Halladay] and I."
Halladay and Hamels have pitched well this season, but the Phillies believe they need more pitching, despite an offense that has been incredibly inconsistent. That is why it is interesting Philadelphia could trade right fielder Jayson Werth, who teams have been scouting recently.
There is some thought the Phillies must trade Werth to clear salary and acquire prospects to trade for Oswalt or Haren. The Phils also don't think Werth will be back after the season, so they would prefer to get more than two compensatory Draft picks for him should he sign elsewhere as expected.