The A's announced on Wednesday that 22-year-old left-hander A.J. Puk, their top prospect and MLB Pipeline's No. 32 overall prospect, will miss the entire 2018 season after undergoing successful Tommy John surgery to repair the ulnar collateral ligament in his left arm Tuesday. The surgery was performed by Dr. Neal ElAttrache in Los Angeles.
Puk will begin his rehab in Arizona on Thursday. He was expected to be promoted to the Majors within the first few months of the regular season after pitching well during Cactus League play, which he opened with 10 consecutive scoreless innings before allowing four runs in his last inning during his final outing on March 15.