The team announced Friday that Olson has undergone a "successful" hamate excision surgery on his right hand after injuring it Thursday against the Seattle Mariners in Tokyo. Olson's injury came on a foul tip.
Last season was Olson's first full campaign in the majors, and he played in all 162 games for the A's. The 24-year-old earned the American League Gold Glove for a first baseman, becoming the first Athletic to take home the award since 2012. Olson's 29 defensive runs saved were 19 more than any other player, per MLB.
The A's will start this season banged up elsewhere, too, as top pitching prospect Jesus Luzardo has been shut down for four to six weeks with a rotator cuff strain, per Susan Slusser of the San Francisco Chronicle.
Per Daniel Brown of The Athletic, Luzardo was progressing toward making the A's starting rotation.
Oakland will turn to 30-year-old Mark Canha, who has been with the A's since 2015, in Olson's absence. Canha appeared in 122 games in 2018, batting .249 with 17 home runs and 52 RBI. For reference, Olson's batting average last season was .247 to go with 29 home runs and 84 RBI.
However, evidenced by the Gold Glove Award, the A's will miss Olson most on defense. Olson led the league in 2018 with 1,403 putouts.
The A's were a surprise in 2018 with a 97-65 record, eventually losing to the New York Yankees in the AL Wild Card Game. Olson was a huge part of Oakland surpassing expectations and will continue to be a foundational piece once he's healthy again.
Per the Orthopaedic Journal of Sports Medicine (h/t Jessica Kleinschmidt of NCS Sports Bay Area), injuries to the hamate in a total of 41 baseball players resulted in players returning within three-to-seven weeks with a median return of five weeks.