According to Washington Post writer Chico Harlan's post entitled, "Guzman out of tonight's lineup", at the "Nationals Journal":

"When batting against Giants closer Brian Wilson in San Francisco last series, a pitch hit Guzman in the thumb. Since then, he's had a little discomfort, and today, he decided it had become too much to play through. The team took an X-ray earlier today, but the Los Angeles team doctor hasn't yet been able to take a look at it..."

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