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5/21/2013 3:16 A.M. ET

Needing more rest, Werth won't return Friday

SAN FRANCISCO -- Manager Davey Johnson revealed that Jayson Werth has had a setback in his recovery from a hamstring strain and that he won't be ready to return from the disabled list as expected Friday.

"I got kind of an alarming report from our doctors that he's going to be awhile longer," Johnson said. "I'd probably say up to two weeks. I don't know, it depends on how it progresses."

The plan was to have Werth play in a few games at Triple-A Potomac this past week, but he was lifted after just three innings and two at-bats Wednesday. Johnson said the organization has decided to rest Werth for the time being after looking at recent results of a second MRI.

"I think he was rushing it," Johnson said. "Hearing from Jayson, he felt like with something wrong with his hammy, it's a light strain, that he could play through it. He started to realize that your hamstring's going to take a little more time. He doesn't want something to happen to him like it happened to Wilson Ramos. So we'll take a step back on it."

Mattheus to disabled list with broken hand

SAN FRANCISCO -- Nationals reliever Ryan Mattheus is expected to miss several weeks with a fractured right (pitching) hand after he slammed it into his locker following Sunday's 13-4 loss at San Diego. Making matters worse, Mattheus didn't reveal the injury to manager Davey Johnson until Monday afternoon after playing catch, when it was too late to call up reinforcements.

As such, Mattheus will be placed on the 15-day disabled list and outfielder Eury Perez will be sent down to Triple-A for pitchers Fernando Abad and Yunesky Maya, who are expected to be with the Nationals by Tuesday.

Mattheus was steamed after giving up five runs Sunday and slammed his hand into his locker after the game. Johnson said there wasn't inflammation initially, but Mattheus tried to play catch Monday afternoon and it swelled up to where he couldn't throw the ball.

"It was a little late at the time," Johnson said. "He felt real bad about it, but I wish he would have said something of what he did."

Johnson said he knew Mattheus' hand was broken at first glance. Initial fluorescent lighting tests on the hand were inconclusive, but X-rays revealed the fracture. Johnson said the team doesn't have an early timetable for his return, but his best guess was that it would take four to six weeks.

Mattheus has been a key part of Washington's bullpen since the 2011 season. Before his last outing Sunday, his ERA was just 2.35, but it skyrocketed to 4.96 when he gave up five runs in one inning. Lefty reliever Zach Duke, who made a spot start for Ross Detwiler on Monday, said it will be up to the entire bullpen to pick up the slack.

"We'll see the situations that we get put in," Duke said. "It changes kind of the dynamic out there, but like I said earlier, we'll find a way to get through it and get people out and win games."

Knee improved, Harper back in action

SAN FRANCISCO -- Following two days off to rest his left knee, Bryce Harper returned to the Nationals lineup for Monday's series opener at the Giants.

Harper played in two games at San Diego on Thursday and Friday but had to sit out the weekend tilts due to discomfort. After doing some light running and outfield work, Harper told manager Davey Johnson he was ready for game action.

"It's something you don't like doing. Don't run into a wall at 100 miles an hour," Harper said. "You're going to feel something this day, you're going to feel something that day. Just trying to keep up on my knee and see what happens."

While Harper was inserted into the third spot of the lineup as the right fielder, his manager said the young slugger wasn't quite 100 percent yet.

"He's still got some swelling in there and he's receiving a little treatment," Johnson said. "He was moving around a little bit better yesterday afternoon, acting like he wanted to go out there and hit something."

Harper said he doesn't know if it will be a lingering issue that will stay with him for an extended period of time, but he acknowledged that he might have to take extra caution when he's on the basepaths.

"It was more just of running on it, sliding and things like that," Harper said of when he felt discomfort in San Diego. "I think that the slide is going to hurt the worst. If I bang it up or something, I'm right back to square one. Hope I don't do that. ... We'll see how I feel after the game tonight and go from there."

Slumping Espinosa sits for another game

SAN FRANCISCO -- For the second straight contest, Steve Lombardozzi replaced Danny Espinosa as Washington's starting second baseman Monday night. Lombardozzi was penciled in as the second hitter in the order vs. the Giants, with Espinosa mired in a 1-for-30 slump in his past seven-plus games.

Manager Davey Johnson said he had a "good talk" with Espinosa recently, noting that the infielder is struggling a bit mentally at the plate.

"I think he's a little beat up right now," Johnson said. "I hate to just sit him out, but he's certainly not doing things he knows he's capable of doing. So it's frustrating for him and he feels like he's letting everybody down. But he's trying to do his best. Sometimes just getting away from it a little bit helps."

Espinosa entered 2013 following two seasons where he hit .242 and averaged 19 home runs, 61 RBIs and 159 games per season. But his current skid has lowered his average this season to .163 with three homers and 12 RBIs, while he has just three walks against 38 strikeouts.

Johnson admitted he's "surprised" that Espinosa isn't improving on his past two seasons but is confident that the 26-year-old will turn it around.

"How you handle adversity is a large part of your success," Johnson said. "We'll get through this. Coming in this year I felt like Danny was a key guy, and if he started doing the things that he's capable of doing, it could make the year a whole lot of fun. I still feel that way."

Johnson was noncommittal when discussing if Espinosa would be back in the lineup Tuesday. Entering play Monday, Lombardozzi had started each of the past eight contests (six in left field, two at second base). He's batting just .212 (7-for-33) in that span, but three of those hits came in Sunday's 13-4 loss to the Padres.

Another notable lineup change was catcher Jhonatan Solano making his first start since Wilson Ramos went on the 15-day disabled list with a hamstring strain Wednesday. Solano figures to have a tough time keeping his job when Ramos returns, as veteran Kurt Suzuki is also entrenched as one of the team's fixtures behind the plate.

"I'm very happy to be here again," Solano said of his recent promotion from Triple-A. "I'm grateful and I hope that I prove myself this opportunity and help out any way I can."

Alex Espinoza is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.