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5/30/2014 11:24 P.M. ET

Harper stepping up workouts with injured thumb

WASHINGTON -- Nationals left fielder Bryce Harper has started participating in minor strengthening and flexibility workouts without a brace on for the torn ligament in his left thumb he sustained on April 25.

The 21-year-old slugger has also started hitting with one hand in the cage and has continued to work out and lift weights during his time out.

"He's doing all the things that he can possibly do outside of the thumb," manager Matt Williams said.

Williams said it is still early in the rehab process and the injury is still healing. As a result, the manager is proceeding with caution and taking it slow in regards to the extent of Harper's activity.

"He's progressing," Williams said. "It takes a while to heal that, though. I think he's really right on track."

Zimmerman bats four times in first rehab game

WASHINGTON -- Third baseman Ryan Zimmerman went 0-for-3 in four plate appearances for the Class A Potomac Nationals on Friday night in the first game of his Minor League rehab assignment as he makes his comeback from a broken thumb.

In his first plate appearance in the first inning, Zimmerman -- who batted third as the designated hitter -- drove in a run on a sacrifice fly to right field. He grounded out twice and flied out in his next three at-bats against the Salem Red Sox.

"We'll see how he comes out of it tomorrow, and how he feels in the morning," Nationals manager Matt Williams said. "We'll make a determination tomorrow what he's going to do."

The game went into extra innings tied at 4, and Zimmerman was due up in the bottom of the 10th, but Williams said the team told the slugger he couldn't have a fifth turn in the batter's box. Khayyan Norfork pinch-hit for Zimmerman and won the game with sacrifice fly to center field.

"Of course it happens that way," Williams said. "It always does."

Zimmerman took batting on practice Wednesday afternoon for the first time since fracturing his thumb on April 12. Williams said Zimmerman took batting practice again on Thursday and looked good.

"It's a question of his timing and feeling good at the plate and seeing some live pitching," Williams said. "I think he's close."

Zimmerman is expected to remain Potomac's designated hitter for a couple of games before moving into the field in order to avoid any relapses. After that, he could play left field, first base or third base. Zimmerman will play all three positions once he returns to Major League action.

During Thursday's off-day, Zimmerman worked out at third base without any issues. Zimmerman worked out at first base on Wednesday, which was also his first time taking ground balls since the injury. Two weeks before that, Zimmerman spent time practicing in left field.

"It's important for him to play all over the place," Williams said.

The Nationals have an off-day on Monday, and Williams said he hopes to get eyes on Zimmerman that day in Potomac for the team's series finale against Salem.

"A player's never going to tell you the truth," Williams said. "So it's good to see him and see what his timing looks like at the plate."

Williams didn't rule out a Tuesday return for Zimmerman, though he said that would be "awfully early." Zimmerman generally doesn't need many at-bats to return to form, as he displayed during Spring Training.

"Being off that long is difficult," Williams said. "But we'll see."

Nats struggling with runners in scoring position

WASHINGTON -- The Nationals entered Friday having lost six of their past seven games and averaging fewer than three runs during that stretch.

A large part of the team's struggles have resulted from offensive lapses with men on base. During the seven-game span, the Nationals are hitting .127 with runners in scoring position.

"When we're rolling, there's a lot less pressure in those situations. You're not as concerned about it," said first baseman Adam LaRoche, who returned from the 15-day disabled list on Sunday. "You know we're going to have more opportunities. You know that if you don't get it done, the guy behind you will get it done. When you're not, when you're up there at the plate knowing that this may be our only opportunity to score, it absolutely makes it tougher. And that's what we're fighting for now."

In an 8-5 extra-inning loss to the Marlins on Wednesday, the Nationals stranded the bases loaded on two separate occasions and finished the night 2-for-11 with runners in scoring position.

In the bottom of the eighth inning, with the game tied at 4, walks to outfielder Nate McLouth and pinch-hitter Scott Hairston, along with a bunt single from Denard Span, loaded the bases with the Nationals' No. 2-4 hitters -- Anthony Rendon, Jayson Werth and LaRoche -- due up.

Rendon and LaRoche both put together quality at-bats and fouled off a number of pitches, while Werth received a good pitch to hit, but the trio ultimately went down in order, spoiling a tremendous opportunity to take the Nationals' first lead of the night.

"Especially if you're not scoring a lot of runs, you can put too much pressure on yourself in that situation," said McLouth, who went 4-for-4 Wednesday night, including a two-run double in the sixth inning. "But usually it works best when you just relax and take the same approach you would with nobody on base."

Worth noting

• Right-hander Blake Treinen, who missed his last start against the Marlins on Tuesday after the game was postponed because of rain, allowed two hits in two scoreless innings to close out a 9-2 series-opening win against the Rangers on Friday night.

Williams said the Nats would push back his next bullpen session because he saw action on Friday night. He'll be ready for his next start, which has yet to be scheduled.

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