Scherzer will start against the Miami Marlins on Monday night and Werth is back in the Nationals' lineup for the first time since early June, batting seventh and starting in right field.
Washington optioned outfielders Rafael Bautista and Andrew Stevenson to Triple-A Syracuse to clear the roster spots.
Scherzer, 12-5 with a 2.25 ERA in 24 starts this season, hasn't pitched since Aug. 13, when he left a start and then sat out a game with neck spasms. He then was placed on the 10-day disabled list.
Werth, 38, has been sidelined since going on the 60-day DL on June 4 with a left foot contusion. Werth, who has played several minor league rehab games in the past two weeks, batted .262 with eight home runs and 18 RBIs in 47 games before the injury.
"Probably have some work to [do] with stamina, playing every day, but the foot feels good. I feel good," Werth told reporters before Monday's game. "I'm here to help. My eyes are still on the prize. I want to win, I want to win a World Series. I think we've got the team to do it."
Werth showed off just how good he was feeling by hitting a two-run homer in the bottom of the fourth inning -- his first home run since June 2.
Information from The Associated Press was used in this report.