Andrew McCutchen sprained his left knee during a rundown in Monday night's game between the Philadelphia Phillies and San Diego Padres.
McCutchen had to be helped off the field and was taken to the clubhouse for examination.
"I didn't feel it pop or anything," he said. "Something felt uncomfortable, something that made me grab my knee and go down. I've had an ACL injury before, and I know what that feels like. This didn't feel like that."
McCutchen will have an MRI on Tuesday.