Athletics first baseman Dan Johnson will begin the season on the disabled list after being diagnosed with torn cartilage in his left hip, manager Bob Geren said Thursday. Johnson was injured Monday in a collision at first with Colorado's Yorvit Torrealba. He was originally diagnosed with a strained hip flexor and listed as day-to-day, but additional tests revealed the tear. The A's gave no indication how long Johnson would be out, but the 27-year-old Johnson could be sidelined up to three months.