Hart experience swelling in his knee during off-season workouts and examinations uncovered a tear in the meniscus of his right knee.
Dr. William Raasch, the Brewers' team physician, repaired the torn meniscus and debrided the knee joint, removing damaged tissue to help healing. Recovery time is expected to be four months.
Hart has played his entire nine-year major league career with the Brewers, hitting .276 with 154 home runs and 508 runs batted in. He hit .270 with 30 home runs and 83 RBI in 149 games last season.
He is in the final year of a three-year, $26.5 million contract and would be a free agent after the 2013 season.