Reddick suffered the injury while making a catch in the visitor's bullpen in the top of the fifth inning. He was replaced at the plate by Mark Canha -- who later delivered the walk-off hit -- in the bottom half of the frame.
"My back locked up and started spasming out," Reddick said. "After the play I went back and watched it. From what I gathered, it looked like it happened from me avoiding the ball boy, who didn't move one bit. Gotta have a talk with him because it kinda made me move a little awkwardly.
"Nothing serious. Hopefully something that's just day to day. I probably won't start tomorrow, get some more treatment done so I can be ready to go Tuesday."
Reddick was 0-for-2 before exiting and finished the series 1-for-14 after collecting eight hits in his previous 18 at-bats.
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.