The MRI substantiated the diagnosis that Contreras has a flexor pronator strain on the inside of his right elbow. Amaro said he will be shut down from throwing for 10 days and then a program of rehabilitation will be determined after that period.
Contreras was placed on the 15-day disabled list on Monday and right-hander Michael Stutes was elevated from Triple-A Lehigh Valley.
"It was a Grade 1 strain, which is very mild and good news for us," Amaro said prior to Tuesday night's game between the Phillies and D-backs at Chase Field. "We're going to shut him down for about 10 days from throwing. Hopefully we can get him back in about three to four weeks pitching [in the Majors]. It's positive news. You don't want to go to the DL, but it's better than the alternative [possible surgery]."
Contreras suffered the injury this past week.
With regular closer Brad Lidge on the disabled list indefinitely because of a sore right shoulder, Contreras was moved into that role. Contreras had pitched in eight games, saving five in his five opportunities. He pitched five times in seven games from April 15-21, including three in a row, although that trio of games was broken up by a rainout.
His last appearance was this past Thursday night in a game he saved at San Diego. Right-hander Ryan Madson saved the games on Friday and Saturday, and with Contreras down, Antonio Bastardo came on in the ninth to save the game on Sunday after Roy Halladay threw 130 pitches.
Madson, the third option, is now the closer.
Lidge, who is expected to be out until the All-Star break, will see Phillies team physicians later in the week with the hope of at least beginning a program of soft toss, Amaro said.
"He feels pretty good," Amaro said about Lidge. "He's kind of champing at the bit right now. We want to make sure that [the doctor] sees him before he starts throwing."