Johan Santana is unlikely to pitch again this season after a magnetic resonance imaging exam revealed inflammation in his lower back.

General Manager Sandy Alderson said the injury would not require surgery. He said Santana, who was placed on the 15-day disabled list retroactive to Aug. 18, was prescribed "rest, medication, and intermittent exercise."

Santana, 33, first experienced soreness during his last start Aug. 17, and complained to team trainers when the pain did not dissipate.