Max Scherzer hasn't pitched since Sept. 30 when he left his final regular-season start with what he referred to at the time as a "small tweak" in his right hamstring.
The reigning National League Cy Young winner was scheduled to pitch Game 1 against the Cubs, but was pushed back to Game 3 to provide him extra time to build more strength and endurance in his hamstring.
Scherzer won his only start against the Cubs this season and is 3-1 in six career starts against Chicago.
The Cubs overcame being no-hit for 5 2/3 innings in Game 1 against Stephen Strasburg to pull out a 3-0 victory to take an early series lead.
But after the Nationals scored five times in the eighth inning in Saturday's 6-3 victory to even the series.
Chicago will counter with Jose Quintana, who will make his postseason debut. Quintana, who was acquired from the crosstown White Sox in a midseason trade, will face the Nationals for the first time in his career.