"Even if you are pinch-hitting, you can do damage it getting out of the box, hitting a double or whatever it is," Williams said. "We'll have the doctor read it and give us his thoughts."
Espinosa sustained the injury against the Phillies on Sept. 14. After walking in the 11th inning, he injured the hamstring while scoring the winning run, according to Williams.
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 Tuesday, Espinosa was hitting .240 with 13 home runs and 37 RBIs.
• With Monday's opener postponed until Thursday due to rain, Williams adjusted the rotation for the next four days.
Right-hander Max Scherzer will pitch on regular rest Wednesday, followed by Tanner Roark and then Jordan Zimmermann, who needed an extra day because of a stiff neck, according to Williams. Stephen Strasburg, who is currently the team's most dominant pitcher, will pitch Saturday against the Phillies.
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.