"I think he dove on that ball and kind of aggravated it a little bit," Johnson said. "Afterward, he was limping a little bit. Seemed to be still running OK."
Harper pinch-hit in the nightcap, grounded out to shortstop in the eighth inning and didn't appear to be limping.
Harper missed the entire month of June with bursitis in his left knee. The Nationals sought a second opinion from renowned specialist Dr. James Andrews, and Johnson said in June that the bursitis could return at any moment.
"Bursitis, it could come back with one slide," Johnson said on June 22. "It could come back bumping into the wall. But just, I mean, is it going to get any worse from regular playing? That's the only thing I have concern with."
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. Tom Schad is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.