Hardy sat out Monday night's game against the Boston Red Sox - the third straight game he has missed with back spasm.
Hardy said he took some groundballs and swings but wasn't healthy enough to play. He was scheduled to fly to Baltimore for tests and a possible cortisone shot.
The Orioles entered the night with a 9 1-2 game lead over the second-place New York Yankees in the AL East.
Hardy is batting .281 with nine homers and 52 RBIs for the season. He was replaced in the lineup by Ryan Flaherty.