Harper was examined by team doctors in Washington, and manager Davey Johnson says Monday that tests showed inflammation but no structural damage. The 20-year-old slugger will take oral medication and sit out the first two games of a four-game series against the Mets.
Johnson says he hopes Harper can play after that, but it will depend how he feels.
Harper, the NL Rookie of the Year last season, was scratched from the lineup Saturday in Miami and hasn't played since. The slugger is batting .273 with 19 homers and 49 RBIs during an injury-plagued season.
The Nationals, on the fringe of the NL wild-card race, aren't sure when Harper will rejoin the team.