Rodriguez started the game and went 0-for-3 with a strikeout before leaving after six innings. He was replaced by Wil Nieves. Rodriguez initially told the team trainers about the problem earlier in the game.
Manager Jim Riggleman noticed Rodriguez was struggling while running to first base after the catcher hit into a double play to end the sixth.
"That last at-bat that he had, I was watching him as he hit first base, and I felt he looked a little tender, so I checked with him and he said, 'Yeah, it's pretty tight.'" Riggleman said.
Riggleman said Rodriguez will not play against the Dodgers on Saturday. Nieves will get the start. Rodriguez has been one of the hottest hitters for the Nationals, batting .423 with seven RBIs.
"The back is OK. It was tight all day," Rodriguez said. "I tried to loosen it up today. The third time up, it was very tight. I didn't want to take any chances, but I'm all right."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.