Tracy, who underwent surgery on May 28 to repair a torn right groin muscle, was making his third appearance with the P-Nats when he felt discomfort running out of the batter's box. The 32-year-old infielder was 0-for-4 as the designated hitter Friday night and is now hitless in nine at-bats at Potomac.
Johnson said Tracy is taking Saturday off to get some treatment, and the Nats are hopeful Tracy can return to action quickly. In 32 games before the injury, Tracy was the Nats' best hitter off the bench, batting .265/.327/.510 in 49 at-bats.
"That's a pretty major injury," Johnson said. "[With] scar tissue, the body tends to over-heal. He probably broke a little bit of that. Hopefully with a day off, if it is just some adhesions breaking loose, hopefully he'll be fine. But we'll know more after today."
Johnson added that outfielder Xavier Nady will also head to Potomac on Saturday for a rehab assignment. Nady was placed on the DL on June 25 with tendinitis in his right wrist, retroactive to June 24.