(Julio Cortez/AP)

Johnson had planned to leave Werth in Viera when the Nationals travel to Kissimmee for their spring training game Saturday. Johnson does not expect Werth to miss a significant number of spring games, “but it’s not something I’m taking any chances with,” Johnson said. “I know he worked out and hit a lot in D.C. So I’m not worried about him.”

Werth had not shown any signs of back trouble prior to missing today’s workout. The Nationals have otherwise experienced no injuries this spring training.

Werth, 32, is trying to regain the form that convinced the Nationals to give him a seven-year, $126 million deal in December 2010. Upon arriving at spring training this year, Werth said his disappointing 2011 season should not define his tenure in Washington.