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5/19/2014 7:46 P.M. ET

Zimmerman says outfield work just for conditioning

Williams doesn't rule out using third baseman in outfield if situation arises

WASHINGTON -- Before Monday's game against the Reds, Nationals third baseman Ryan Zimmerman was seen working out in left field for the second time in a week, leading to speculation that his future is in the outfield.

However, Zimmerman said he was working in the outfield for conditioning purposes. He can't take ground balls because of his fractured right thumb. None of the coaches have told him to do outfield drills. The Nationals don't want him to take ground balls in the infield because the thumb is not 100 percent.

"It's fun to get outside … do something, run around be out there with my teammates," Zimmerman said.

On the other hand, manager Matt Williams didn't rule out Zimmerman playing the outfield in a Major League game one day.

"I cannot [rule it out]. I wouldn't say the same thing about Kevin Frandsen or Zach Walters, who hasn't played out there since college," Williams said. "I'm not going to say that we are definitively not considering [Zimmerman in the outfield]. I think he is a wonderful athlete. If there is a point during the game and we have nobody left and he has to play left field or right field or center field, he can do it. That's where we sit."

Zimmerman could play a different position by next year. The team is seriously considering making him its first baseman and Anthony Rendon its third baseman, a position he is playing since Zimmerman went on the disabled list.

With Gio on DL, Treinen to start Thursday

WASHINGTON -- Nationals manager Matt Williams announced that right-hander Blake Treinen will replace left-hander Gio Gonzalez in the rotation. Gonzalez was placed on the 15-day disabled list Sunday with shoulder inflammation.

Treinen has performed well in his two stints with Washington as a starter and reliever. He is 0-1 with a 0.77 ERA in four games. The last time he pitched for the Nationals was May 6 in an 8-3 loss to the Dodgers. In that game, he pitched five innings and allowed three unearned runs.

Because of the outing against the Dodgers, Williams felt Treinen deserved to start against the Pirates on Thursday.

"It's hard to deny him that opportunity after how he pitched against the Dodgers. It's really hard," Williams said. "He was on a limited pitch count. He pitched really well against them. He has been building from there. He has been normal [rest], so he'll be prepared."

Treinen is 2-0 with a 1.96 ERA in six starts for Triple-A Syracuse.

LaRoche takes grounders as he continues rehab

WASHINGTON -- Nationals first baseman Adam LaRoche took ground balls for the first time since he was placed on the disabled list on May 11 because of a right quad strain. According to manager Matt Williams, LaRoche will soon take full batting practice on the field and start running the bases.

"I want him to go get a grounder that's just reactionary, potentially turn and have to go into right field to try and catch a popup," Williams said. "It's hard to simulate that. … When that is, I don't know."

LaRoche is eligible to come off the DL on Sunday. It's not known if he will go on a rehab assignment before he plays in a Major League game.

Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.