Espinosa's hamstring issue occurred against the Phillies last Monday. After walking in the 11th inning, Espinosa sustained the injury while scoring the winning run, according to Williams.
"He felt it [in Philly] and he was really non-functional the next day," Williams said. "We tried to get him a spot where he could pinch-hit. We can run for him since we have extra guys. Other than that, he hasn't been able to go."
Espinosa has been a valuable player off the bench. He has been able to play all four infield positions and the corner spots in the outfield. Entering Monday, Espinosa was hitting .240 with 13 home runs and 37 RBIs.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All theTime. He also can be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.