Kansas City, Mo. ? Kansas City Royals second baseman Mark Grudzielanek will have surgery on his left knee for the second time since March, and the team doesn’t know how long he’ll be out.

Team physician Dr. Steve Joyce will perform the procedure today. Grudzielanek, who won a Gold Glove Award last season, has been one of the Royals’ steadiest hitters this year. He leads the team with 18 doubles and drove in seven runs in the three-game series last weekend against Philadelphia. On Sunday, he was 3-for-5 and matched his career high with five RBIs.

The Royals also said Thursday that right-hander Brandon Duckworth had joined Grudzielanek on the disabled list because of a strained muscle in his side. He was hurt while pitching against St. Louis on Wednesday night.

The team called up lefty Neal Musser and outfielder Shane Costa from Triple-A Omaha. Costa had just been sent down the day before. The 36-year-old Grudzielanek had arthroscopic surgery on the same knee in March to repair torn cartilage.

Manager Buddy Bell refused to speculate on how long Grudzielanek might be out.

“We don’t know how significant that is until Dr. Joyce gets in there and sees the extent of the damage,” he said. “I guess he hyperextended it or something. There’s a small divot in there, a flap that is the problem. We’re not sure what the extent of the damage is.”

Duckworth experienced a sharp pain in his left rib cage Wednesday night after coming out of the bullpen and throwing just two strikes.