Harper said he felt good, and based upon how he feels Sunday, the Nats will determine whether he could play in games in the instructional league or return to the Nats' lineup.
"He's close. He's very close," manager Dusty Baker said. "We just have to talk to him and get a true evaluation of how he feels. And true is the key word.
"He's chomping at the bit to come back. We're chomping at the bit to have him back, but we have to do what's best for him and us in the long run as well."
The Nationals flew in a pair of Minor League pitchers, right-hander Steven Fuentes and left-hander Alex Troop -- who was selected in the ninth round of the Draft in June -- to serve as Harper's competition for this latest test. Harper was joined by infielder Stephen Drew and outfielder Brian Goodwin, who are both working their way back from their abdominal and groin injuries, respectively, to make their own push for the postseason roster.
Harper took batting practice on the field for the first time Sunday and participated in his first sim game Tuesday; he also has taken fly balls in right field, and he ran the bases to test the bone bruise in his hyperextended left knee and strained calf.
"The biggest thing for me is just trying to see where my timing's at, see how it feels," Harper said. "It takes time to get back in the swing of things. Baserunning felt good the other day, throwing to bags, things like that. But yeah, everything felt good, and we'll see where we're at and go from there."
If he makes it through this latest hurdle unscathed, Harper could be activated to play in regular-season games during the final week. Or the Nationals might want to keep him in a controlled environment and send him to their complex in West Palm Beach, Fla.
Hours before the Nationals' game against the Mets on Saturday, the focus was on Harper as he continues to clear every potential hurdle in his rehab. He has not played since injuring his leg on Aug. 12. Washington has aspirations for a deep postseason run, and having Harper healthy and in the middle of its lineup is crucial.
"He would really send an influx of confidence into this team to have him back," Baker said.