General manager Mike Rizzo said Martinez had a minor cardiac catheterization Monday in Washington.
Martinez, who turns 55 on Sept. 26, experienced chest pains during Washington's home game Sunday against Atlanta, left in the sixth inning and was taken to a hospital.
Bench coach Chip Hale will manage the Nats during Martinez's absence. Hale said Martinez texted him Monday's starting lineup.
"I'm sure he'll give us a call after the game if he's up,'' Hale said. "I know he's been through a battery of tests. Hopefully he's feeling good.''
First-base coach Tim Bogar will be in the dugout and assistant hitting coach Joe Dillon will replace Bogar at first.
The Nationals saw their top National League wild-card lead shrink to a half-game over the Chicago Cubs after Monday night's loss.
Martinez is in his second season managing the Nationals. After winning 82 games last season, the Nats have matched that total this season with 13 games to play.
Martinez had a 16-year MLB career with nine teams.
The Associated Press contributed to this report.