Braves doctors said they would wait a couple of weeks for the swelling and pain to subside before deciding on a course of action. Either Medlen will go through a period of rehabilitation or have Tommy John surgery, which appears likely. Recovery from the surgery generally takes one year.
Medlen left Wednesday night's game against the New York Mets after 4 1/3 innings. He gave up four hits and two runs.
"When it happened on one pitch like that, you know something happened. After the pitch it [elbow] felt awful," Medlen said.
"It's discouraging. We're going to try the rehab thing and see if that helps out before we jump to conclusions. Anytime you have an arm injury, it's a steep hill to climb," he said.
The right-hander showed no sign of discomfort against the Mets before throwing a pitch outside of the plate to Jose Reyes with one out in the fifth. Medlen took a couple of hops off the mound, and manager Bobby Cox quickly came out of the dugout.
Medlen left his previous start Friday in Cincinnati after he was hit on the inside of his right forearm by a pitch from Johnny Cueto. He said that had nothing to do with his current injury.
"I wouldn't have threw myself out there if I knew I was going to hurt myself. I felt fine warming up," said Medlen, who was 6-2 with a 3.68 ERA in 31 games, 14 starts.
The Braves recalled right-hander Cristhian Martinez from Triple-A Gwinnett to take Medlen's spot.
Martinez was 4-1 with a 3.28 ERA at Gwinnett, including two starts. He pitched in seven games earlier in the season with Atlanta and had a 5.06 ERA in 10 2/3 innings.