The procedure removed the bone. There's no timetable for Olson's return, and he'll presumably be placed on the injured list before Oakland's home opener on March 28.
Olson suffered the injury when he foul-tipped a ball during his final at-bat of Thursday's game against the Seattle Mariners. He then hit a single and came around to score, but Mark Canha replaced him at first base the following inning.
The 24-year-old appeared in all 162 regular-season games last season, his first full big-league campaign, and slashed .247/.335/.453 (116 OPS+) with 29 homers, 33 doubles, and 84 RBIs.
He also led all first basemen in putouts, defensive runs saved, and ultimate zone rating to earn a Gold Glove.