The division-leading Washington Nationals put third baseman Ryan Zimmerman on the disabled list Wednesday with a right hamstring strain.
Zimmerman left Tuesday's game against the Rockies in Denver in the sixth inning after hitting the first-base bag hard trying to beat out a ground ball.
Infielder Zach Walters was recalled from Syracuse of the Triple-A International League.
Manager Matt Williams says Zimmerman had an MRI on Wednesday and remains "pretty sore."
Zimmerman missed 44 games with a fractured right thumb earlier this season but has played well since coming off the disabled list June 3.
"He's swinging great, playing great, but we have to deal with it," Williams said Tuesday.
The Associated Press contributed to this report.