Davis was nauseous and vomiting after the team's West Coast trip, Showalter said, so head athletic trainer Richie Bancells sent him home to avoid the illness from spreading.
"That's one of the things about traveling all over the country," Showalter said. "I hope it's an isolated case. We'll see."
Steve Pearce is filling in for Davis at first base, with outfielder Delmon Young serving as the designated hitter and batting in Davis' usual No. 5 spot.
Showalter didn't totally rule out the possibility that Davis could serve as a pinch-hitter, though. The first baseman was told to go home and drink fluids, and if he feels better later in the evening, he could return to the stadium.