Infielder Andy Parrino was recalled from Triple-A Sacramento to take Lowrie's place on the roster.
Lowrie had said Thursday he expected to go on the DL since it had become clear the injury would prevent him from playing every day.
The shortstop originally began feeling discomfort after taking a grounder off his finger against the Tampa Bay Rays on Aug. 4. He played in five games since, but an MRI on Tuesday revealed the hairline fracture.
Lowrie, 30, is hitting .238 with a .671 OPS this season.
Parrino, 28, has played in five games with the A's in 2014. He's hit .286 with a .363 on-base percentage in 90 games for Sacramento.
The A's entered Friday at 73-48, the best record in baseball.
- Ben Estes