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8/14/2013 1:19 A.M. ET

Ramos aggravates hamstring while running to first

WASHINGTON -- Nationals catcher Wilson Ramos has served two stints on the disabled list this season with a left hamstring strain, and he aggravated the injury during Tuesday night's game against the Giants. Manager Davey Johnson said that Ramos was examined by trainer Lee Kuntz, and team doctor Wiemi Douoguih and that the injury is "not too bad."

"It's the same time on that same left hamstring," Johnson said after the Nationals' 4-2 win over the Giants. "Obviously, they think he might be day to day. But we'll have to see. I doubt if he's available tomorrow."

Johnson said that Ramos tweaked the hamstring while running to first base in the fourth inning. The 26-year-old hit a ground ball that ricocheted off pitcher Madison Bumgarner's mitt to third baseman Pablo Sandoval, and the catcher unsuccessfully tried to beat the throw to first base. Johnson removed Ramos from the game after the 77-minute rain delay in the fifth inning, and replaced him with Kurt Suzuki.

Ramos missed 15 games in April because of the hamstring strain, then played for two weeks before aggravating the injury and missing an additional 44 games. He said last month that he was still anxious about tweaking the muscle a third time, and was being extra cautious. He has also been sticking with a preventative treatment routine, including stretching and workouts in a pool.

"You have to be smart," Ramos said on July 24. "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."

Flu keeps Harper out of Nats' lineup vs. Giants

WASHINGTON -- Left fielder Bryce Harper was scratched from the Nationals' starting lineup on Tuesday because he had the flu, according to manager Davey Johnson.

Trainer Lee Kuntz told Johnson that Harper spent most of the team's day off on Monday sleeping, adding that the 20-year-old couldn't eat much. However, Harper did feel well enough to participate in batting practice before Tuesday's series opener against the Giants.

Johnson said that he would have started a healthy Harper against Giants left-hander Madison Bumgarner despite the fact that Harper is batting .172 against lefties this season.

"He's 3-for-9 with a home run [against Bumgarner]," Johnson said. "But we'll give him the day off."

Harper actually entered the game as a pinch-hitter in the eighth inning against reliever Santiago Casilla, and was intentionally walked in his only at-bat.

Right fielder Jayson Werth, meanwhile, returned to the lineup Tuesday after leaving Sunday's game in the seventh inning with a right knee injury. Werth banged his knee while sliding home against the Phillies. He did not have an X-ray on the knee, and Johnson said that the injury was likely just a bruise.

"He looked like his cheerful old self today," Johnson said, smiling.

Detwiler runs, but no baseball activities yet

WASHINGTON -- Nationals starter Ross Detwiler will not resume baseball activities for at least another week, but he was sprinting in the outfield at Nationals Park before Tuesday's game. General manager Mike Rizzo still hopes that the left-hander will return to the Nats' rotation this season.

"He's progressing well," Rizzo said. "Now he can ramp up a throwing program. It's a routine that we use whenever a pitcher gets shut down for that long."

Detwiler has been on the disabled list since July 7 with a herniated disc in his back. Doctors prescribed a month of rest, which has now passed, as well as anti-inflammatory medicine. Manager Davey Johnson said that he wanted to see how Detwiler's back responded to the running before proceeding.

Johnson also said that Ross Ohlendorf threw a side bullpen session on Tuesday and will make a second Minor League rehab start on either Thursday or Friday. Ohlendorf pitched three innings at Triple-Syracuse on Saturday, but Johnson said the right-hander would need one more rehab start before returning to the Nationals.

Ohlendorf will throw between 50 and 60 pitches in his upcoming appearance, Johnson said. Barring any setbacks, the hurler will likely replace Taylor Jordan, who will soon hit his team-imposed innings limit, as the Nationals' fifth starter.

Worth noting

• Closer Rafael Soriano recorded his 30th save of the season on Tuesday night, joining Tyler Clippard, Drew Storen and Chad Cordero as the only Nationals to notch at least 30 saves. Soriano has now recorded more than 30 saves in three of his past four seasons.

• Johnson had a minor back procedure on Monday, which included a cortisone injection. The procedure took about an hour.

"I feel better," the manager said. "I'm real sore from where they jabbed me, but other than that, I'm good."

• Rizzo deflected a question about the Nationals' managerial search before Tuesday's game.

"We're not discussing the manager for next year," Rizzo said. "We're still focused on this season and looking forward to playing tonight against the Giants. That's as far into the future as I'm looking."

• The Gulf Coast League Nationals won their 16th straight game on Tuesday and improved to 40-6 this season. The organization's lowest-level affiliate has 11 more wins than any other team in the GCL.

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