Bryce Harper in as injury replacement

Washington Nationals rookie outfielder Bryce Harper has been named to the National League All-Star team, replacing Miami Marlins outfielder Giancarlo Stanton, who will undergo arthroscopic surgery on his right knee on Sunday.

"(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."

Harper is the fifth rookie in this year's All-Star Game, a major league record.

Pittsburgh Pirates outfielder Andrew McCutchen will take Stanton's spot in Monday's Home Run Derby.

The Marlins will now not have a representative in the game. Guillen joked that Tony La Russa, the NL All-Star manager now working for Major League Baseball, didn't have his phone number except "when he calls me for fines."

Stanton, a first-time All-Star, started Saturday's 3-2 loss at St. Louis but was removed for a pinch hitter in the third.

Stanton, who singled and scored on Justin Ruggiano's two-run homer in the second, began the day with a .282 batting average, 19 homers and 50 RBIs.

"He's a big bat," Guillen said. "This is our power hitter, the RBI guy. I think everybody out there has got to step it up a notch and try to cover the space."

But Guillen said the Marlins won't rush things, adding: "He's back when he's back. I think we have to be careful with him."

Hill described Stanton's mood as "encouraged."

"It's a common surgery, a lot of people have done it and come back quickly," Hill said. "We're hopeful that will happen with Giancarlo."

Both Guillen and Hill thought the Marlins had enough talent to survive until Stanton gets back. Outfielder Emilio Bonifacio is expected to come off the 15-day disabled list from a sprained left thumb that has sidelined him since May 20 after the All-Star break.

Information from The Associated Press was used in this report.