Miller intends to get a second opinion on his elbow Tuesday, manager Torey Lovullo told reporters.
Miller, off to a good start after an awful 2016 season, left in the fifth inning of Sunday's game against the Los Angeles Dodgers.
He had thrown four scoreless innings but walked the first two batters in the fifth and allowed a double. Miller threw one more pitch before being removed from the game. He is 2-2 with a 4.09 ERA in four starts.
Lovullo said the MRI conducted Monday showed inflammation.
"What that second opinion will do is allow us to get more information without speculation," Lovullo said. "When that happens, I'll be able to give you more of an answer."
Speaking before Monday night's game against San Diego, Miller said the doctor did not provide him with a lot of details.
"Just kind of looked at the MRI a little bit, saw something was there, some inflammation and stuff," he said.
If a tear or partial tear is found, surgery might be necessary.
"I guess there's some kind of chance," Miller said.
Lovullo said he hasn't decided who will take Miller's spot in the rotation. Miller's turn comes up Friday at home against Colorado. Archie Bradley could be shifted from the bullpen, but his success as a reliever may cause Arizona to bring up a starter from the minors.
Arizona recalled right-hander Silvino Bracho from Triple-A Reno to take Miller's roster spot. Bracho is 0-1 with two saves in six appearances with the Aces. He has struck out 12 and walked one. The one run he has allowed was unearned.
Miller was acquired in a much-criticized trade with Atlanta before last season, sending outfielder Ender Inciarte and two top prospects -- No. 1 draft pick Dansby Swanson and right-handed pitcher Aaron Blair -- to the Braves.
Miller went 3-12 with a 6.15 ERA. He came into spring training with a fresh attitude after an offseason of work.
"Extremely unfortunate for Shelby and for this organization," Lovullo said. "He's worked so hard to get back on his feet again. He was throwing the ball very, very well, but we understand these things happen."
The Associated Press contributed to this report.