Davis was placed on the disabled list Wednesday but revealed he has been bothered by discomfort in his hip and the surrounding areas for months, dating to when he was nursing a strained left quad during a DL stint from May 14-June 18.
"It took a while to get him back and I thought once we got him back we were over that hurdle, but I guess it got progressively worse and he wasn't saying a whole lot about it," manager Bob Melvin said. "But recently, probably the last couple of weeks, it just got to the point where he wasn't comfortable swinging or running, so it kind of came to a head then."
Davis mustered only six hits in his final 45 at-bats, bringing his season average down to .229. He hit just three home runs for a club that had hopes of a solid bounceback season from him, already missing 33 games along the way with the quad injury.
Davis, 28, posted a .775 OPS in 32 games before the injury but struggled upon his return, with a .537 OPS over his final 40 games.
"I know he felt like he really didn't have the type of bat speed he's used to having," Melvin said.
Davis has one more year of team control, though the A's could opt to non-tender him this offseason -- a scenario that, already probable given his hitting woes, seems all the more likely in the wake of his impending surgery.
Rookie Mark Canha will continue seeing the bulk of playing time at first base in Davis' stead. Stephen Vogt also remains an option, as does outfielder Jake Smolinski, who has been getting in work at the position in recent days.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.