Rizzo is hoping that Xavier Nady and Roger Bernadina can step in and make up for the loss of Werth. For now, Nady and Bernadina will platoon in left field, while Bryce Harper will be the everyday right fielder.
"With the injury to Werth, there's an opportunity for somebody on this current roster to take the next step, not only in his career, but to help the ballclub," Rizzo said. "We have in-house candidates that can handle the job. We are looking for someone to step up and take command of it."
By June, the Nationals are hoping that Michael Morse can return to left field and give Washington much-needed power. Morse has yet to play a game during the regular season because of a torn left lat (shoulder) muscle. He is not able to perform any baseball activities for another two weeks.
Last year, Morse led the team in almost every offensive category.
"Can we continue to play at the level we are playing at without Michael Morse? I think the answer is yes," said Rizzo. "It's going to take other players to step up and perform to their abilities. If we do that, then I think we can get by without Michael Morse until he gets back into the lineup."
With left field occupied for the time being, left fielder/first baseman Tyler Moore will continue to come off the bench as a pinch-hitter.
Asked if it was unfair for Moore to sit on the bench, Rizzo said, "For his development, he should be playing. But, again, he is a 25-year-old player that has performed admirably at each level that he has played on. He started off very strong in Triple-A."
"We think he is big league ready at this time. He is on this ballclub to help us win games. If I thought for one minute it was going to set back his development, he wouldn't be here. And I don't think that is the case."
In five big league games, Moore is 2-for-7 (.286). Moore, who is ranked No. 14 on MLB.com's list of Top 20 Nationals prospects, was hitting .286 with seven home runs and 20 RBIs for Syracuse before getting recalled.
In 2010 and 2011, Moore has hit a combined 60 home runs with 201 RBIs for Class A Potomac and Double-A Harrisburg.
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.