Werth left Monday's 7-6 loss to the Marlins in the seventh inning after sliding into second base awkwardly trying to stretch a single into a double.
''He's a little swollen today,'' Nationals manager Matt Williams told reporters before the game. ''He'll certainly be available off the bench tonight, but we're not going to start him.''
Nate McLouth received the start in Werth's place.
''Hopefully by the time the game starts, I'll be moving around pretty good,'' Werth said. ''Tape it up, if he needs me, I'll play and be available.''
Williams added that Werth could be in the starting lineup on Wednesday.
''I don't think it's anything serious, but it's a little swollen, a little sore,'' Williams said.
Werth is batting .284 with 12 home runs and 58 RBIs for the Nationals.