The team announced Scherzer was put on the IL with a minor rhomboid strain. The injury is located in the same area as the inflammation under his right shoulder that landed the right-hander on the injured list for 19 days this month.
Scherzer won seven straight starts in June as the Nationals attempted to climb back into playoff contention after a 19-31 start to the season. The ace returned from the IL on July 25 and gave up three runs in five innings against the Colorado Rockies. He underwent an MRI the next day that revealed the ailment.
Scherzer's move to the injured list is retroactive to July 26, meaning the star pitcher could return as soon as Aug. 5.
The three-time Cy Young Award winner has a 9-5 record and 2.41 ERA in 20 starts this season. He ranks first in the National League in strikeouts (189) and strikeouts per nine innings (12.66), and second in ERA (2.41) and strikeout-to-walk ratio (7.56).
The Nationals recalled right-handed pitcher Erick Fedde from Double-A Harrisburg in a corresponding move. Fedde was scheduled to start Tuesday night against the Atlanta Braves in Scherzer's spot in the rotation.
Fedde, 26, is 1-1 with a 3.40 ERA in 13 games (eight starts) for Washington this year. His last start came June 24 against the Rockies when he allowed one earned run on three hits in four innings.