The Nationals announced about 45 minutes before the game that Werth, who was slated to bat sixth and play right field, wouldn't start. He wore a boot on his right foot Monday night and said he "definitely" couldn't have played, although he added, "I don't think it's serious."
Nationals manager Davey Johnson said he first noticed the injury Sunday, when Werth pinch-hit, ran to first and limped a bit afterward. Werth has dealt with similar injuries before, and he hoped to be able to play Tuesday night against the Giants, although, he joked after the Nats' 14-2 romp, "They don't need me anyway."
Werth has been dealing with general soreness, particularly in his legs, since returning from the disabled list Aug. 2. The outfielder left a game in Houston on Aug. 6 due to leg soreness, but he was back in the starting lineup Wednesday after Johnson kept him out of the starting lineup for precautionary reasons last Tuesday.
The Nationals are 9-0 in games Werth has started since coming back from the disabled list. In his place Monday, Michael Morse moved from left to right field, shortstop Danny Espinosa was bumped up from seventh to sixth and Roger Bernadina was slotted into the lineup, batting seventh and manning left field.
"Hopefully it's something that in a day or so, he's fine. I didn't want to play him," Johnson said. "Hopefully he'll be OK to go [Tuesday]."
Morse, meanwhile, jammed his right thumb during batting practice and was replaced by Tyler Moore in the fifth inning. Morse said afterward he felt fine and expected to be back in the lineup Tuesday.