Montgomery, 23, on Wednesday was demoted to Double-A Northwest Arkansas from Triple-A Omaha after going 3-6 with a 5.69 ERA in 17 starts for the Storm Chasers.
"He's actually throwing fine," Royals general manager Dayton Moore said. "We just want to get him back there with [pitching coach] Larry Carter and work on some things. The organization just felt it was the right thing to do. Just give him a breather and re-start a little bit."
Carter worked with Montgomery in 2010 with the Naturals, when he was 5-4 with a 3.47 ERA in 13 starts. The lefty struggled in his two seasons with Omaha, going a combined 8-17 with a 5.46 ERA. That's tough going for a guy who made a strong bid for the Major League club in Spring Training 2011.
"We're trying to get him more downhill and power his fastball in the zone," Moore said. "We just think getting back down there will be beneficial to him."
The Royals moved left-hander Chris Dwyer from Northwest Arkansas to Omaha. Dwyer, 24, was 5-8 with a 5.25 ERA in 17 games for the Naturals.
MLB.com's Prospect Watch ranks Montgomery as third and Dwyer seventh in the Royals organization's top 20.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.