Dr. James Andrews repaired a torn capsule in the free agent's shoulder last week, MLB.com's Peter Gammons reported.
"I understand that I have to sit out this season as I rehab the shoulder," Harden said. "That's fine. I know what I have to do, and I am hopeful that at this time next year I'll be healthy and ready to try to come back with someone. To be honest, I'm relieved to have it over and move forward. It's been a long time since I felt the way I should. It's been five years of inconsistency."
Harden's shoulder injury dates to 2007, and his innings total has declined progressively every season since '08, when he threw 148. He was limited to 82 2/3 last year while pitching in his second stint for the A's. It was his third team in the past three seasons.
Harden went 4-4 with a 5.12 ERA last season and was nearly traded to the Red Sox before the deal fell through due to the right-hander's medical records. Harden is 59-38 with a 3.76 ERA in his career, always showing strong ability when he is healthy enough to pitch.
"I hope and believe that if I do the work and everything Dr. Andrews tells me to do, I can have the game be fun again," Harden said.