The strain has been described as "very slight" and "grade one-ish" by general manager Mike Rizzo, reports CSNWashington. Werth attempted to do leg curls earlier on Friday, but his hamstring went into spasms.
Werth, 33, has been out since May 2 when he left that day's game after feeling tightness in his hamstring. Because he has not played since then, the Nationals will be able to backdate his DL stint, making him eligible to return as early as May 18. The Nationals are confident that he will be back at full health by that time.
The right fielder had been a game time decision for much of the past week. He was very close to being in the starting lineup against the Tigers on May 8, but the wet weather during that series caused the Nationals to keep Werth out as a precaution.
The Nationals have said they will call up one of two outfielders from Triple-A Syracuse: Either Eury Perez or Jeff Kobernus. Perez spent a short time in the majors in 2012 and has hit .346/.352/.439 in 23 minor league games this season. In 31 games, Kobernus has hit .371/.402/.468.
Both players profile similarly. Neither has particularly strong on-base skills or much power. They are contact hitters who both are very dangerous threats on the basepaths. The difference between the two is their defensive reliability. Perez has played center field his whole career while Kobernus was a second baseman his first four seasons in the minors and has been playing outfield in an attempt to make him a utility player.
The Nationals will likely decide on which player is called up later Friday night as they are expected to officially make the DL move after tonight's game against the Cubs.