Johnson tried for more than two months to address his shoulder trouble non-surgically, and got as far as throwing off a mound. However, the rehab didn't progress as well as he or the team hoped, so he will have an operation.
"It's just not responding," Mozeliak said on Tuesday afternoon.
Johnson first encountered trouble early in Spring Training. He was diagnosed with tendinitis and a rotator cuff strain in his throwing shoulder, and was shut down. More recently, the club has called Johnson's condition shoulder capsulitis.
After extensive rest, Johnson began a throwing program. However, after re-evaluation by doctors, including Dr. Elattrache, the decision was made for Johnson to undergo surgery.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.