"(Stanton) might be out for a month or six weeks, that's what I think," Marlins manager Ozzie Guillen said after a 3-2 loss at St. Louis on Saturday. "Hopefully less. We're better off that way because that kid couldn't do anything."

General manager Mike Hill said surgery had been discussed as an alternative if Stanton had difficulty playing. He said the procedure to remove a loose body in the knee is fairly routine.

"It was just discomfort," Hill said. "And we knew that once we had tried it, that if it flared up again, surgery was the logical option."

Harper, 19, entered Saturday's game hitting .283 with eight home runs, 25 RBIs and 42 runs scored in 61 games. He will be the youngest All-Star position player in history, and the third youngest overall after pitchers Dwight Gooden and Bob Feller.

"I don't have words to explain it right now," Harper told The Washington Post. "It's exciting to go. I'm excited to get there and be around all of the top guys in the country, of course, and the top guys in baseball. I'm going to take it all in and try to enjoy it with my family and just be as mellow and calm as I can."