"It's just gotten worse and worse," Sweeney said.
Billy Butler, the organization's top hitting prospect, will have his second tour with the big-league club this season. KC's 2004 first-round pick hit .243 in 37 at-bats in May.
Butler will pinch-hit the next five games and then DH every day until Sweeney returns. KC considered other players but Butler was the only option who was on the 40-man roster that could be called up and then sent back to Minors without passing through waivers.
"We talked about calling somebody up but our roster is so blocked right now that if we brought somebody up we would have to put them through waivers," manager Buddy Bell said. "I don't know if anyone could have picked him up or not, but we don't have a lot of depth."
Sweeney, who has not been able to run at full speed in recent games, had a cortisone shot Sunday. On Monday, he and Bell opted to put the DH on the disabled list.
"We were contemplating to DL him after Sunday's game just because it wasn't getting any better," Bell said. "The medical people suggested to him that a couple weeks would do him some good."
Sweeney had a MRI and will have some more tests Wednesday. Bell and Sweeney said the veteran shouldn't miss more than two weeks.
The schedule, though, allows Sweeney to miss only a few contests. Because the Royals have two series in National League ballparks that don't use the designated hitter, Sweeney would see only pinch-hit opportunities anyway.
"If there is a best time, this is it," Sweeney said. "I would really miss six games, seven games max."
Butler was batting .291 with 13 homers and 46 RBIs when he was recalled. Considered Major League-ready at the plate, the organization is still trying to find him a position. For the past month, Butler has played first base for Triple-A Omaha, but is not considered an option to start at first in the Majors.
"He will play first in an emergency if we need him, but he is not progressing at that rate yet," Bell said.
Butler, who finished his first Major League stint 2-for-21, now feels more comfortable in the Majors.
Rotation stays: KC will stay with its normal rotation the next few days. After the off-day Thursday, Jorge De La Rosa will make his regular turn on five days' rest and Brian Bannister will pitch Saturday.
The team had considered moving De La Rosa or sandwiching either Gil Meche or Brian Bannister between Odalis Perez and Scott Elarton, two pitchers who haven't worked deep into games recently. Bell said that won't happen.
"We are going to keep it the same right now. We don't really have any options right now," Bell said. "[Pitching coach Bob McClure] and I have talked about it and there is no sensible way of doing it. We have to get some innings out of a few guys and if we don't, it will force us to do something, but right now we didn't really feel like we need to."
No lineup changes: The Cardinals made a very late change to their starting rotation, announcing Brad Thompson as Tuesday's starter. Kip Wells was supposed to start the game and wasn't informed of the move until he reached the ballpark Tuesday. Bell, though, didn't make any last minute changes to his lineup.
"No, not really," Bell said. "The problem would have been if it was a left-handed, right-handed [switch]. Pretty much it was the same lineup whether it was Wells pitching rather than Thompson."
Bunts: After hitting another homer, John Buck has 13 this season, tied with the Indians' Victor Martinez for the Major League lead among catchers. Buck also ranks first in slugging (.591) and second in OPS (.952) among backstops.
Entering this year, Buck had never hit more 12 homers in a season, slugged higher than .424 or enjoyed an OPS above .704.
"I have been feeling more comfortable with two strikes and can take a pitch early or in the middle of the count, or take a pitch that is maybe a strike but not the strike I am looking for," Buck said. "It's a combination of those things that is making me feel comfortable."
Royals Rundown: Triple-A Omaha lost, 6-2, to Nashville. Tyler Lumsden, considered one of the best pitching prospects in the Royals' organization, allowed six runs (four earned) on eight hits in six innings. Lumsden is 5-5 with a 5.40 ERA this season, but has allowed more than three earned runs twice in his last nine starts. ... Double-A Wichita fell, 12-4, to Tulsa. Danny Christensen permitted four runs on five hits in 4 2/3 innings. ... Class A Wilmington was off because of its all-star break. ... Class A Burlington was also off because of its all-star break.
Player of the day: Jake Blalock, Wichita. Blalock had two hits, including his first home run for Wichita. He was acquired from the Double-A Frisco Rough Riders earlier this season and is batting .171 with eight RBIs in 76 at-bats. The outfielder was picked by the Phillies in the fifth round of the 2002 draft.
Coming Up: KC completes its I-70 season series against a former teammate on Wednesday. Todd Wellemeyer, designated for assignment by the Royals this season, will pitch against his former team. Ace Gil Meche will counter for KC. First pitch is set for 7:10 p.m. CT.
Conor Nicholl is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.