Manager Joe Torre said Ramirez would be out at least two days and possibly the entire weekend series against the Nationals.
Los Angeles was leading 3-2 on Thursday night when Ramirez grounded a single up the middle with one out in the sixth inning. He slowed down as he approached first base and immediately left the game.
The 12-time All-Star went into the game hitting .421. He reached 1,800 RBIs on Wednesday, after recording his 2,500th career hit on April 10 at Florida.
Ramirez is tied with Hall of Famer Mike Schmidt for 14th on the career list with 548 home runs.
Information from The Associated Press was used in this report.