Because of the off-day on Thursday, Johnson believes Harper will be back in the lineup on Friday against the Marlins. Harper doesn't have any plans to get an MRI, and the origin of the injury is unknown.
It has been an injury-plagued season for Harper, who missed more than a month because of an injury to his left knee after banging into the wall at Dodger Stadium on May 13.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the Time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.