The Braves said Medlen will be re-evaluated Monday.
"We have to wait and see," Braves manager Fredi Gonzalez told reporters in Port St. Lucie, Fla. "Obviously when he came out of the game, anytime a pitcher walks off the mound and meets you at the foul line you're worried. But I think after everything kind of settled down, we're optimistic that it's nothing really major."
Medlen grabbed his elbow after throwing the first pitch to Matt Clark with two outs in the bottom of the fourth inning Sunday. He quickly left the field with a trainer.
"I talked to him 30 seconds after he came inside, after I made the pitching change," Gonzalez said. "He wasn't in good spirits then. He was really, really worried. But after he got settled down and the trainers looked at him and Mets doctors looked at him, I think he was in better spirits. I did not talk to him after those conversations he had with the doctors and trainers, but our people told me that he was in little better spirits.
"Keep our fingers crossed. But I feel a lot better after talking to our medical people. We might be OK."
Medlen, who had Tommy John surgery in 2010 and missed most of the following season, was 15-12 with a 3.11 ERA last year. The 28-year-old is slated to start Opening Day for Atlanta.
Before leaving with the injury, Medlen had allowed one run on three hits, striking out two.
"He was executing pitches," Braves catcher Evan Gattis told reporters. "The next thing you know, I didn't know what he had grabbed or anything, but for whatever reason I kind of knew it was his arm, or thought so. It's never a good sign, never a good feeling, to be out there and see a pitcher walking off the mound like that."
ESPNNewYork.com's Adam Rubin and the Associated Press contributed to this report.