Cleveland ? All-Star first baseman Mike Sweeney was placed on the 15-day disabled list Thursday by the Kansas City Royals.

The move was made retroactive to June 19, one day after Sweeney left a game against Minnesota because of tightness in his upper back.

“Mike was examined this morning and the diagnosis is he has nerve irritation where the neck and upper back come together,” Royals trainer Nick Swartz said.

Swartz said it would be at least a week before Sweeney could get back to on-field activities. Sweeney traveled to Kansas City late Wednesday night and was examined by team Dr. Steve Joyce Thursday morning.

Sweeney tops the AL Central-leading Royals in most offensive categories, including homers (12), RBIs (50) and batting average (.321).

Sweeney’s .477 average with runners in scoring position leads the majors, and he ranks among the AL leaders in average, walks and on-base percentage.

To replace Sweeney on the 25-man roster, the Royals recalled second baseman Brent Abernathy from the minors. They also recalled left-hander Les Walrond, a Kansas University product, from Omaha and optioned right-hander Ryan Bukvich to their Triple-A affiliate.

Swartz said Sweeney’s final at-bat June 18, where he lost the grip on his bat as he struck out, was the telltale sign of the problem. But the trainer theorized the cause may have happened in an odd way.

“One thing we have come up with, yeah, it sounds humorous, but he hit a home run and during the celebration at the plate he gets the tapping on the head,” Swartz said. “Think about it, you’ve got guys smacking your head, what’s your first reaction? You tip your head down. That could have been the beginning of it.”

Manager Tony Pena said the loss of the Royals’ top offensive player was just one more hurdle the young club will have to overcome.

“This has been our ballclub all season,” Pena said. “We didn’t have Carlos Beltran early and we played well.”