Hardy, who missed six games in April with lower back spasms, said he was feeling pretty normal Tuesday afternoon.
"Obviously I want to play, but I think it's probably the smart thing to do," said Hardy. "I felt pretty good the day that I hurt myself in April in Detroit, so just to be safe, take one more day and go from there."
Hardy batted in the top of the seventh Monday, but he did not return for the eighth inning, with Ryan Flaherty taking over at shortstop. Afterward, Hardy said the humidity could have played a factor, telling reporters he can lose up to eight pounds on a hot day, and he smiled Tuesday when asked if he had been hydrating a lot.
"I'm probably about six pounds overweight right now from all the stuff I've been drinking," Hardy said.
The O's, who have lost Matt Wieters and Manny Machado to season-ending surgery, are also currently playing without infielder Steve Pearce.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Facebook and Twitter @britt_ghiroli. David Wilson is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.