Harper, who has been battling hip issues recently, aggravated the issue during batting practice before Saturday's game. Harper was scratched with what manager Davey Johnson said after the game was inflammation in his hip.
"He's going to go to see the doctor tomorrow, figure out what it is, treat it, and he'll meet us in New York, hopefully," Johnson said.
Depending on the results, the 20-year-old could be out for an extended period of time, according to the Washington Post.
Harper is hitting .273 on the season, with 19 home runs and 49 RBIs.
Information from The Associated Press was used in this report.