Stanton was hurt in the 10th inning of Monday's 4-3, 15-inning win over the New York Mets.
He said after the game that he heard a pop in his leg and that he fears the injury might be serious. He's scheduled for an MRI on Tuesday.
He hit a tapper in front of the plate and clutched his right hamstring just before he crossed first base, trying in vain to beat the throw. He then fell face-first to the turf and pounded the grass in anger.
Stanton rose slowly and limped off the field. He was replaced in right field after the inning.
The 2012 National League slugging leader had shaken an early-season slump recently, hitting his first home run Saturday and two more Sunday.