The right-hander was placed on the 10-day injured list last week after tweaking his groin in the first inning of his start on June 11 against the San Francisco Giants.
The three-time Cy Young winner is 5-4 with a 2.21 ERA this season.
The Nationals placed right-handed reliever Kyle Finnegan on the 10-day injured list with a left hamstring strain in a corresponding move, which was made retroactive to Monday.
Finnegan is 3-2 with a 3.86 ERA in 33 appearances this season.
The Nationals have won eight of their last 10 games entering Tuesday to move to three games under .500 at 33-36.