Zimmerman rigorously threw today and hit off a tee at about 75 percent force, Johnson said, and felt no discomfort. The 27-year-old will take part in batting practice tomorrow, and the Nats will see how he feels.
Zimmerman is eligible to come off the disabled list Sunday. Johnson said he "wouldn't be averse" to activating Zimmerman on Sunday, but the Nats are more likely to play it safe with their All-Star and wait until Tuesday, following their off-day.
"It's a miniscule chance (of Zimmerman playing Sunday)," Johnson said. "But I think Zim's feeling more positive today."
First baseman Adam LaRoche, meanwhile, is still being held out because of a sore right oblique.
LaRoche, who injured the oblique diving for a ball two nights ago, swung at about 30 percent today, Johnson said, but still felt discomfort.
Asked if LaRoche would need to go on the DL, Johnson confidently responded, "No." He then paused.
"I'm hoping he won't," he added.
Chad Tracy will get his second straight start at first base tonight.