"He had some discomfort in his elbow earlier," Amaro said. "It got to the point where it became a real issue for him."
The lefthander had an MRI exam Thursday that revealed the injuries. He will have more testing done to determine the severity of the injuries. Surgery could be needed to repair the ligaments and tendons.
If the sprain in Moyer's ulnar collateral ligament is severe enough, he would require Tommy John surgery. At age 47, it's not a stretch to consider Moyer declining the surgery and calling it quits. He will be a free agent after the season.
But Moyer had two surgeries this past off-season and returned to full health before opening day to earn a spot in the Phillies' rotation. The difference then was the injuries weren't to his pitching elbow.
"He's going to be out quite some time," Amaro said.
Moyer is the active career leader in wins with 267, which ranks 36th all-time. He is one behind Hall of Famer Jim Palmer.
Cole Hamels said losing Moyer would be tough.
"He's a mentor to all of us," Hamels said. "Obviously we'll be fortunate enough to have him around even though he's not pitching. But there's always something you can learn from him when he's pitching."
In the off-season, Amaro said he didn't expect Moyer to be ready for opening day following his four stays in the hospital over the winter. But Moyer was healthy for the beginning of spring training and won a roster spot.
In 19 starts this season, Moyer is 9-9 with a 4.84 ERA. He became the oldest pitcher ever to throw a shutout on May 7, a two-hitter against the Braves.