CLEVELAND -- Cleveland Indians designated hitter Travis Hafner underwent arthroscopic surgery on his right knee Thursday at the Cleveland Clinic and is expected to miss at least one month and possibly six weeks, leaving a sizeable hole in the middle of team's lineup.

The slumping Indians could be without Hafner, who was placed on the 15-day disabled list Wednesday, until after the All-Star break. In the meantime, they'll have to find someone to take his spot as a run producer.

"Hey, we can't just throw our arms up," manager Manny Acta said Thursday. "We have to move on and get on with it. Somebody needs to step up. More guys in the lineup need to do their thing."

Since sweeping the Detroit Tigers last week, the Indians have dropped five of their last six games and have fallen into second place in the AL Central behind the Chicago White Sox, who have won eight straight games and swept three in a row from Cleveland last weekend.

The Indians said Hafner underwent a 30-minute procedure performed by team physicians Dr. Rick Parker and Dr. Mark Schickendantz to clean up frayed cartilage in his knee, which first flared up on him in a May 23 game against the Tigers. Hafner, who will turn 35 on Sunday, is on the DL for the sixth time in his career.

In the final year of his four-year, $57 million contract, Hafner is batting .242 with six homers and 23 RBIs in 39 games.

His injury is just one of several medical issues to slap the Indians this week. Catcher Carlos Santana is already on the seven-day DL with a concussion. His backup, Lou Marson, received stitches in his mouth after being hit by a pitch. And third baseman Jack Hannahan was placed on the DL earlier this week with a strained calf after being sidelined eight games with a sore back.

All-Star shortstop Asdrubal Cabrera just returned after missing three games with a tight hamstring.

The mounting injuries are reminiscent of last season, when the Indians started 30-15, led the division most of the year but crumbled down the stretch amid a rash of players getting hurt.

With Hafner out, the Indians could use outfielders Shelley Duncan and Johnny Damon or third basemen Jose Lopez and Lonnie Chisenhall in the DH role. It's also possible they could promote either Matt LaPorta or Russ Canzler from Triple-A Columbus.

"Everybody on the Triple-A roster is an option," said Acta, who planned to use the off day to evaluate the team's next move.

Information from The Associated Press was used in this report.