"I was really disturbed I wasn't informed that he was having some treatment on his hip," Johnson said. "But every time someone talks to Harp, he said, 'I'm fine.'"
Harper, who was running the bases gingerly during Monday's game, had a single and walk against the Phillies.
Johnson said he believes Harper will start Tuesday night against the Phillies.
Harper wouldn't say much about his injury. He plans on playing as many games as he can before the season ends.
"We have a month left. I'm going to play as hard as I can. I'll worry about [the hip] in the end," Harper said. "If I was hurting, I would come out of the game. I feel good."
It has not been an injury-free season for Harper. He missed more than a month due to a left knee injury 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.