Nationals manager Matt Williams said Harper was at the Nationals' complex earlier in the day, getting ready to play against the New York Mets.
''He came in, did a little bit of light swinging in the cage and he's still not feeling good, so we sent him home. I think he'll be OK to go'' on Friday, Williams said.
Harper was ill Wednesday and scratched from the travel roster for the game against St. Louis in Jupiter, Florida.
''It's one of those rites of spring that everybody goes through at one point or the other during spring training,'' Williams said. ''He just happened to have it the last couple of days. But he's good.''