"Jayson saw the doctor, and after he got an MRI, it looks like he's headed toward the disabled list with a very slight strain of his hamstring," general manager Mike Rizzo said on Friday. "The three grades -- this would be a Grade 1-ish type of strain. ... He'd be able to come off [the disabled list] Saturday the 18th, and we'd anticipate him being able physically to come off the 18th."
Rizzo didn't rule out that dehydration could be the culprit.
"The [dehydration] issue is the issue," Rizzo said. "We think it could be cramping, could be just cramping because of the [dehydration], so we're going to get that under control and see where he's at and just be cautious with it."
Werth said he felt bad that manager Davey Johnson had to deal with 24 players for more than a week. He said the hamstring is getting better, but the team is being cautious, which he understands.
"You go out there with the way it is and you might make it [worse] pretty quickly," Werth said. "We err on the side of caution, but at the same time, at this point, I think it's necessary.
"Hopefully, it will be another seven days, so hopefully I could come off after the 15 days and be fine. The most frustrating point about the whole thing is, I feel pretty good. … There is just a little cramp there at times. And cramps lead to bigger and worst injury."
In the meantime, the Nationals called up center fielder Eury Perez, ranked by MLB.com as the organization's No. 7 prospect. Perez is off to a great start, hitting .346 with a home run, six RBIs and seven stolen bases for Triple-A Syracuse.
Before the decision to promote Perez was made, Jeff Kobernus, ranked as the No. 16 prospect, was another candidate to be called up. He can play the infield and outfield and is also off to a great start for Syracuse, going 47-for-127 (.370) with a home run and 16 RBIs. Last December, the Tigers selected Kobernus in the Rule 5 Draft, but he was sent back to the Nationals last March.
The Nationals were thinking about bringing Kobernus to the Major Leagues last summer, but shortstop Ian Desmond was able to recover from a left oblique strain, and Kobernus remained in Syracuse for the rest of the season.