Michael Taylor, who started in left field, was shifted to center field, while Matt den Dekker went to left field. Span has been dealing with back problems most of the season, but the team can't seem to fix the problem.
"We have changed programs, he is strengthening, he is stretching," manager Matt Williams said. "The trainers are doing everything they can possibly do. So we will just continue to monitor, continue to do what we are doing. Some days it's great, some days it just pops up on him."
Escobar injured the hamstring while beating out an infield single in the third inning off Reds right-hander Anthony DeSclafani. Escobar was replaced by Dan Uggla, who played second base, while Danny Espinosa made the switch from second to third base.
Williams vowed the team is not going to feel sorry for itself because it continues to deal with injuries.
"Not going to do it. We have games to play," Williams said.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the Time. He also can be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.