"It's pretty sore tonight. Get the MRI, get some results tomorrow and see where we're at," manager Matt Williams said. "It's concerning. Anytime you have to leave the game with a hamstring injury, it's concerning."
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. "We'll see how he feels tomorrow and what the doctors say."
Zimmerman left the game after hitting the first-base bag hard trying to beat out his grounder.
"Guy's just coming back from the DL, getting his swing back and you hate to see that," Adam LaRoche said. "Cross our fingers it's nothing major."
The Associated Press contributed to this report.