Update: Harper's injury has been diagnosed as a bruised lat, the Washington Times reports. He'll be re-evaluated by the team's medical staff Thursday.
Recommendation: Manager Davey Johnson said the bruise stemmed from crashing into the wall Tuesday night. Harper managed to join the starting lineup Wednesday but exited after an at-bat in the sixth inning after apparently aggravating the injury while swinging. Consider him day-to-day, but it seems very likely he'll be scratched as a precaution Thursday against the Braves at the very least.