The Braves announced Medlen's surgery after he was examined Monday by Dr. James Andrews in Gulf Breeze, Fla.
Beachy was also examined by Andrews and will now head to Los Angeles to get another opinion from Dr. Neal ElAttrache, the Dodgers' team physician.
Medlen will undergo the second Tommy John surgery of his career after having the elbow ligament replaced in 2010. Beachy underwent the same procedure in 2012 and has endured multiple setbacks since then.
Medlen and Beachy were expected to be stalwarts of the Braves' rotation. After they went down, the team hastily signed free agent Ervin Santana to a $14.1 million, one-year contract.