According to Johnson, Werth has been bothered by left knee and calf injuries, which is the reason he was shifted from center field to right field starting Wednesday night.
"He is getting treatment on it every day," Johnson said. "He had some strange looking blue tape on it [Wednesday] night. I texted him early this morning and asked if he needed a blow, a day off. He texted me back and said, 'I'm fine. I felt stiff yesterday, but I feel good.' So he is in the lineup."
Werth, who signed a seven-year, $127 million contract last winter, has struggled at the plate, hitting .234 with 19 home runs and 56 RBIs. Johnson doesn't believe that injuries played a role in his offensive problems.
Johnson believes Werth has taken on too many roles, including trying to be a leader for the young players.
"I think there are a lot of reasons," Johnson said. "I think he took a lot of responsibility for a young ballclub. Adam LaRoche was out, Ryan Zimmerman was out. He was basically the only veteran in the lineup.
"I think he had to wear too many hats and not worrying about No. 1. I think he is getting over that. I think he is more comfortable and the supporting cast is starting to perform better. So I think everything is getting more normal."