His spot on the roster was taken by infielder Mike Aviles, who was Omaha's hottest hitter with a .338 average and 42 RBIs. He made his Major League debut at shortstop on Thursday night against the Minnesota Twins.
Butler was batting .263 and was not hitting with much power. He had just one home run along with 11 doubles and 18 RBIs.
"It's one of those things," Butler said. "I'm not happy about it. I'm disappointed. It's not where you want to be."
"I don't think anybody's hitting where they want to be. You can point your finger at me and I can be accountable. You know, the past three or four weeks haven't been the best for me, and I'm willing to grind it out and work my way out of it in the big leagues. I'd like for them to show confidence in me to get back out of it in the big leagues, but that's just not the way it works out."
A designated hitter and first baseman, Butler hit safely in his last five games, 5-for-18, but all five hits were singles and drove in no runs. His only home run came on April 14 at Seattle.
Butler, 22, has been considered one of the Royals' rising stars, but with the club locked in a 10-game losing streak and run production lacking, he was sent out to get his stroke back.
Aviles, 27, has played 32 games at second base and 18 at shortstop for Omaha and made six errors. With Tony Pena Jr. struggling at the plate (.160), Aviles was immediately inserted into the lineup in Pena's spot.
"We're not looking at this as a permanent fix at shortstop, but I am going to play him there tonight to see if we can get one more offensive slot and hope it doesn't affect us defensively. We all know what Tony can do defensively," manager Trey Hillman said.
He added that this will give Pena a chance to "take a deep breath" and work on his hitting. Because Pena is out of options, the Royals could not send him to the Minors without first exposing him to waivers.
"We don't want to lose Tony Pena," Hillman said. "We believe he can continue to get better, and Tony is working at it as hard as he can."
Aviles might also fill in at second base for Mark Grudzielanek, who has been out with a sore back. Alberto Callaspo started at second base on Thursday night.
A right-handed batter, Aviles had 10 home runs, six triples and 21 doubles in the Minors. In 213 at-bats, he had struck out just 23 times.
Aviles is in his third season with Omaha. Last year, he batted .296 with 17 homers and 77 RBIs and was named Kansas City Minor League Player of the Year. He also did well last winter in Venezuela, as he batted .299 for Aragua and hit six homers and had 27 RBIs in 56 games.
After playing at Middletown (N.Y.) High and Concordia (N.Y.) College, he was selected by the Royals in the seventh round of the 2003 Draft. That summer, he played for the Surprise Royals in the Arizona League and hit .363, leading the league in runs (51) and doubles (19) in 52 games.
Aviles' contract was purchased from Omaha.
Butler was called up from Omaha on May 1, 2007, for a 16-day stay. He returned to Omaha for another month, was recalled on June 19, and thereafter hit .298 with eight homers and 48 RBIs in 82 games.
Butler is more of a gap plugger than a home-run blaster, but the Royals obviously expected more punch than he's shown so far.
He was batting .302 on April 25 this year, but, in 31 games since, he hit just .231 (24-for-104) with seven doubles and eight RBIs.
"We all know that Billy is better than that," Hillman said, "but he's not squaring balls up at the same ratio. He's not even taking pitches with the same comfort level and balance at the plate."
Hillman wouldn't guess at how long Butler might be with Omaha, where he'll also continue to refine his skills at first base. That spot has been vacated by Ryan Shealy, who reinjured his hamstring and has been rehabbing in Arizona for about two weeks.
Butler was held out of the lineup twice recently, on May 22 at Boston and on Tuesday night against Minnesota. In both games, he was used as a pinch-hitter and singled.
"There's certainly no intention of Billy Butler being the scapegoat, none whatsoever," Hillman said.
Butler didn't seem so sure about that.
"He told me that, too, but it looks different, doesn't it?" he said.
Unlike Pena, Butler had options remaining and Hillman conceded that played into his demotion.
Although Butler began the season as the regular DH, he worked hard at playing first base and was being used more frequently at that position this month. However, Mark Teahen has been playing first base recently, moving in from right field to make room for Joey Gathright in the outfield.
For Butler, the move came just when he thought things were looking up at the plate.
"I was starting to feel better," he said. "The last couple of days I've felt better than I have in the last few weeks," he said.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.