J Pat Carter/AP

Nationals outfielder Jayson Werth, who has already missed 16 days on the disabled list, visited a specialist in Chicago to further diagnose his strained right hamstring, Manager Davey Johnson said. The Nationals long expected Werth to return today, but after a stalled minor league rehab assignment they now do not think he will be ready to play until Friday, when the Nationals return home after their 10-day West Coast road trip.

After Werth played three innings for Class A Potomac on Wednesday, he visited a specialist in New York with whom he has worked closely. He was still feeling tightness when he ran out of the batter’s box, Johnson said, and so Werth another specialist in Chicago.

“He’s a finely tuned athlete,” Johnson said. “He’s got a lot of people to keep him that way. Anytime you have something with a hamstring, that’s not something I want to rush back anyway.”

The Nationals will also be without Wilson Ramos for an extended period, Johnson said. Ramos re-injured his left hamstring Wednesday night. The Nationals placed him on the disabled list immediately. After Ramos received an MRI back in Washington, Johnson believes the Nationals will be without him for longer than the minimum 15 days.

“Anytime it’s in the same spot, it’s worse,” Johnson said.