The former NL MVP had to be helped off the field and was taken to the clubhouse for examination. He was replaced in the lineup by Jay Bruce, who was acquired this week in a trade with the Seattle Mariners.
"I didn't feel it pop or anything," McCutchen 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."
Manager Gabe Kapler said the Phillies will bring up Adam Haseley on Tuesday, and if McCutchen isn't available for the Phillies, "it will sting," he said.
McCutchen, 32, is hitting .256 with 10 home runs and 29 RBIs as a leadoff hitter in his first season in Philadelphia. He was signed to a $50 million, three-year contract during the offseason after finishing last season with the New York Yankees.
McCutchen spent his first nine seasons with the Pittsburgh Pirates, joined the San Francisco Giants last year and then was traded to the Yankees.
The Associated Press contributed to this report.
McCutchen exits game with knee injury
Andrew McCutchen injures his left knee in a rundown during the first inning.