Davey Johnson had said Friday that he expects Harper to start a rehab stint Tuesday at Class A Potomac. Harper, who has been sidelined since May 26 with left knee bursitis, said he thought he needed an extra day or two.
"It just depends how I feel today and tomorrow," Harper said before Saturday's game against the Colorado Rockies. "Monday is an off day, which is good. Tuesday, that's kind of early. I'm thinking Wednesday or Thursday, maybe."
Reporters later informed Johnson of Harper's comments during the manager's pregame media session.
"I'll have a conversation with him about that," Johnson said. "When a player starts playing, it's really up to me, what I think they need. Not up to the player. I'm always trying to do what's best for the player. But at the same time, it's my job to know when they're ready and when they're not."
Entering Saturday, Harper has missed 29 of the Nationals' 73 games. The NL Rookie of the Year ran in the outfield and took swings in the indoor batting cage the previous two days.
"Running after a ball and running on the bases and hitting, I'm full speed, every single day," Harper said. "It's going to be hard playing at 70 percent if they want me to play at 70 percent. I'm not going to do that. I want to come back 100 percent and get back as quick as I can.
Johnson: "The most I'm concerned about is is (Harper) going to be able to bounce back after playing a nine-inning game? He's probably worried about timing and everything being letter-perfect. All that changes from if you're in Potomac. You may never get your timing there because it's a whole new ballgame there, guys don't have command as well as they do up here, and there's a big variation in how they pitch to guys.
"So I'm more concerned about just how they recover from when they come off the DL than I am about what they hit. Since he's never really been on the DL or done rehab, I think his concept might be different from mine."
Before his managerial career, the 70-year-old Johnson played in the majors for 13 seasons.
"I trust players too. They know more about their body than the medical staff," Johnson said. "But when you come back from injury, are you ever 100 percent? But the body has a wonderful ability to heal itself. The more you get the blood flowing, the more you have to heal. Let's get off the DL, guys."
Despite the missed games, Harper, batting .287, remains tied with Ian Desmond for the team lead in home runs with 12.
"It's still going to be sore the whole year, I feel like," Harper said of his left knee. "But daily, it's getting better. I have no pain, which is good. I'm a little sore everywhere else, but that's common. It's good to have no pain finally. To run with zero pain is going to feel great."
Washington has struggled without its left fielder, but their current three-game winning streak has moved the Nationals one game above .500 at 37-36.