Medlen underwent an MRI after leaving Sunday's spring training outing and the diagnosis for a return is uncertain at this point. The 28-year-old had Tommy John surgery on the same elbow in August 2010 and missed most of the following season recovering from the procedure.
"His MRI showed injury to the ligament, but don't yet know the extent," said Braves general manager Frank Wren, who added that MRIs can be inconclusive when a player has had a previous Tommy John surgery.
"A diagnosis would be premature at this point," Wren added. "He will undergo further tests until we seek a second opinion."
With two outs in the bottom of the fourth in Sunday's spring training game against the New York Mets, Medlen threw his first pitch to Matt Clark and could be seen reaching for his right forearm/elbow.
After throwing his next pitch, Medlen hopped off the mound and headed straight for the dugout.
Medlen bounced back after his surgery to go 10-1 with a minuscule 1.57 earned run average before going 15-12 with a 3.11 ERA over 31 starts for the Braves last season.