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7/24/2013 11:55 P.M. ET

Detwiler out a month; Jordan to fill in for now

WASHINGTON -- After the Nationals lost their sixth straight game Wednesday night, manager Davey Johnson revealed that Ross Detwiler will miss a month with a disk problem in his back.

"He's got a little disk problem," Johnson said. "I think it's causing a pinch in the nerve which causes that to spasm."

Johnson said that Detwiler would receive an injection in his back and then rest. The left-hander has been on the disabled list since July 7, and he also missed 24 games earlier this season with a back strain.

Detwiler saw a back specialist in Los Angeles on Wednesday after again being bothered by the injury during an abbreviated bullpen session Saturday.

"He couldn't do a whole lot of running. He usually likes to run a lot, but he didn't do any running before he threw because he felt uncomfortable," Johnson said Tuesday. "It's a problem."

The news creates further problems at the back end of the Nationals' rotation, where rookie Taylor Jordan has filled in while Detwiler and Dan Haren have been out. Jordan has shown progress in each of his first five Major League starts, but he is also on an innings limit after undergoing Tommy John surgery in September 2011.

Johnson said on Wednesday that Jordan has 20-30 innings left before he will be shut down.

"His command is getting better, his slider, which is his third pitch, is getting a lot better, more consistent," Johnson said. "I think [he has] 20-30 more innings. ... But we really haven't had discussions on that."

Over the weekend, general manager Mike Rizzo said that Jordan, like every pitcher in the organization who has had Tommy John surgery, will be shut down early. But he declined to specify how close Jordan was to hitting that limit.

"I know what the parameters are, I know where he's at, and when he gets to that number, that area, we'll shut him down," Rizzo said.

When Jordan reaches his limit, the Nationals most likely will ask long reliever Ross Ohlendorf to be the fifth starter.

Harper, Desmond sit; Rendon gets first start at short

WASHINGTON -- The Nationals' lineup was missing two of its most prominent stars on Wednesday as it looked to end a five-game losing streak.

Manager Davey Johnson said that Ian Desmond has a blister on his left hand and could miss a couple of days. All-Star Bryce Harper also didn't start against the Pirates after recently receiving some treatment on his previously injured left knee, but Johnson expected him to return to the lineup Thursday.

"I might need to check on him a little more," Johnson said of his 20-year-old left fielder. "He hadn't really been in the training room, and that's the good sign. But again, I'm not going to take any chances."

Harper missed Wednesday's game as a precaution after he recently iced his left knee, which caused him to miss 31 games this season. Desmond's blister, while also not serious, could cause the shortstop to miss more than one game.

"It's a big blister," Johnson said. "He got it from a lot of hitting, and when he slid headfirst one time, it just broke. … It was really looking bad [Tuesday] night."

Desmond played in 99 of the team's first 100 games. Entering Wednesday, he had played in more games than any Major League shortstop besides J.J. Hardy of the Orioles (102) and Jimmy Rollins of the Phillies (101).

"It helps because he's such a good player," reliever Tyler Clippard said. "He's come a long way, he's put in a lot of work to get where he's at, and we all see that, especially guys who've been around for a while, and we respect that. … He's out there every day, grinding it out."

With Desmond on the bench, Johnson shifted Anthony Rendon to shortstop and inserted Steve Lombardozzi into the lineup at second. Rendon had never started a Major League game at shortstop, but he said that he grew up playing the position in high school.

"It's easier really for a third baseman to play short than it is for a true second baseman to go over there," Johnson said. "But playing a new position at this level, I think he's doing great. Not only is he learning to play a new position, but the adjustments you have to make up here."

Hamstring feeling good, Ramos playing more frequently

WASHINGTON -- Catcher Wilson Ramos spent two stints on the disabled list earlier this season with a left hamstring strain, missing 58 games. But on Wednesday, he was in the Nationals' starting lineup for the 13th time in 17 games since coming off the DL.

"It feels 100 percent right now," Ramos said of his hamstring. "I don't want to think about my hamstring. Try to clean my mind of that. Right now, I'm still doing my treatment, my exercises in the pool, I'm still doing everything."

Manager Davey Johnson said that Ramos will get the next two days off, including Thursday afternoon's game against the Pirates and the first game of Friday's doubleheader against the Mets. He said that he's been playing Ramos more regularly after trying to ease the catcher back when he first returned in late April.

"If you remember the last time he came off the DL, I went easy with him. [I played him] every other day for about five games, 10 days. And then when I went back-to-back with him, it blew up," Johnson said. "So when he came off this time, I've been playing him."

Ramos said that he's maintained a treatment and exercise regimen since returning July 4 and will continue that regimen throughout the season. He's also being more careful on the basepaths in an effort to prevent future hamstring problems.

"You have to be smart," Ramos said. "I know when I can run 100 percent, try to get a base hit, but it's not necessary with a routine ground ball to go 100 percent. For me right now, I'm trying to run hard, but if it's not necessary, then I won't do it because I don't want to get hurt."

Worth noting

• Detwiler, who has been on the disabled list since July 7 with a back strain, saw a back specialist in Los Angeles on Wednesday. Johnson said before Wednesday's game that he had not heard about the results of the meeting.

• Johnson announced that Jordan Zimmermann will start the first game of Washington's doubleheader against the Mets on Friday. Ohlendorf will pitch in the nightcap.

Tom Schad is an associate reporter for MLB.com. Follow him on Twitter @Tom_Schad. This story was not subject to the approval of Major League Baseball or its clubs.