In the bottom of the fourth inning, Cardinals third baseman Scott Rolen hit a ground ball near the third-base line. Rolen beat Ryan Zimmerman's throw to the bag, but collided with Young at first base. Young was leaning toward the line as he was trying to get the ball. Young remained in the game until it was delayed by rain in the top of the fifth inning.
Young expects to get treatment for his back on Monday and hopes to start against the Dodgers on Tuesday.
"I didn't know [I was hurt] until I took a couple of steps," Young said. "There was nothing to describe. Rolen ran into me. I went for the ball. I must have been on the line, and there was a collision. I moved to the far side of first."
This is Young's second injury this season. He played through a sore Achilles tendon during the early part of May.
The Nationals' hottest hitter, Young entered Sunday's action leading the team in batting average (.302) and on-base percentage (.391). Over his last 11 games, he went 17-for-31 (.548) with a home run and nine RBIs.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.