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Giancarlo Stanton was set to play in next week's All-Star game and participate in the home run derby. Instead, he'll be recovering from arthroscopic surgery on his right knee.

After learning Stanton will miss at least a month, the Miami Marlins will try to end the first half of the season on a positive note Sunday in the finale of their three-game series against the St. Louis Cardinals.

Stanton returned to Miami's lineup Saturday after missing four games, but the return was short-lived. He exited after two innings due to continued problems with his right knee.

Stanton, who leads Miami with 19 homers and 50 RBIs, will undergo surgery Sunday and could miss about a month, according to manager Ozzie Guillen.

"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."

The injury is a major setback for the Marlins (41-43), who had started to turn things around after a 3-17 stretch in June. Miami had won seven of nine after defeating St. Louis 3-2 on Friday, but lost by the same score Saturday.

The Marlins continue to struggle with runners in scoring position after an 0-for-3 effort Saturday. They are batting .232 with runners on second or third, including .197 on the road.

It hasn't helped that they've faced strong pitching from St. Louis (45-40), which has won five of seven. The Cardinals rotation is 4-2 with a 1.85 ERA over its last six games, with each starter going at least six innings.

Kyle Lohse tossed seven innings to earn the win Saturday, with Tony Cruz's two-run triple supporting him.

Joe Kelly (1-1, 3.29 ERA) will get the ball in the Cardinals' final game before the All-Star break.

The rookie right-hander continues to do an admirable job filling in for Jaime Garcia, who has been out a month with a shoulder strain and isn't expected back until August.

Kelly hasn't allowed more than three runs in any of his five starts and has gone six innings in each of the last three.

He surrendered a three-run homer and walked four in a 3-2 loss to Colorado on Tuesday.

"He was not as efficient as he could certainly be, but overall I thought he did a nice job," manager Mike Matheny said. "He kept us in there. He's given us a chance every start. You can't ask for more than that."

Kelly's previous outing came at Miami on June 27, when he gave up two runs and five hits and didn't get a decision in the Cardinals' 5-3 defeat.

Anibal Sanchez (4-6, 4.19) earned the victory in that contest, allowing three runs in seven innings, and will oppose Kelly again Sunday.

Sanchez's last start wasn't nearly as strong, as he gave up six runs and a season-high 11 hits over five innings against Milwaukee on Tuesday, a contest the Marlins lost 13-12 in 10 innings.

Sanchez is 1/3 with a 7.34 ERA in his last six starts, giving up six or more runs three times.

Cardinals slugger Matt Holliday, who extended his hitting streak to 10 games Saturday, is 7 for 14 with two homers and a double off Sanchez. He is batting .444 during his streak.