Kansas City, Mo. ? Mike Sweeney, who had hoped to get back in the Kansas City Royals’ lineup this week, will have arthroscopic surgery on his right knee today.

Sweeney, hitting .245 with seven home runs and 31 RBIs, has been dogged by injury since signing a $55 million contract five years ago. A vigorous offseason yoga program has kept him free of the back problems that had been plaguing him.

He went on the disabled list June 19 because of right knee inflammation. The surgery will be performed by team physician Dr. Steven Joyce.

“We just don’t know how long he might be out,” said manager Buddy Bell.

Sweeney’s tough luck could be a lucky break for 21-year-old rookie Billy Butler, who was called up from Triple-A Omaha to be the designated hitter in Sweeney’s absence. Butler, who homered and doubled and drove in six runs on Monday, was slated to return to the minors when Sweeney returned.

“I think he’s got a lot to learn about his swing,” Bell said. “He’s got a lot to learn about the game in general. But I think he’s also a kid who can learn up here. I don’t think he necessarily needs to go back to Omaha. The problem is that if Mike’s healthy, there’s a good chance we might have to send him back.

“But we don’t have to deal with that right now cause Mike’s not healthy.”