Hughes lasted 4 1/3 innings, allowing four runs (three earned) on five hits with five strikeouts and four walks. He threw 87 pitches, 53 of them for strikes.
There is some cause for concern when it comes to any elbow injury involving Hughes. He missed all of 2006 while recovering from Tommy John elbow ligament replacement surgery.
"It just kind of felt weird when I threw a pitch," Hughes said of his final toss on Saturday night. "I think it's more just precautionary reasons than anything else. I just didn't feel comfortable throwing another pitch, because I had Tommy John before and I didn't want to tear anything. We don't really know anything yet, but maybe we'll find out more [Sunday]."
Later in the inning, Yabuta surrendered a grand slam to Carlos Quentin, breaking the tie to put the White Sox in front, 7-3.
Hughes had made four relief appearances, throwing a total of eight innings for Kansas City, and allowing three runs on six hits (3.38 ERA). Hughes made his debut Sept. 6, tossing 4 1/3 innings of scoreless ball against the Angels -- the longest outing for a Royals reliever during the 2009 season.
Hillman said he was hopeful that the injury was nothing more than inflammation, which would settle down in the next few days.
In other injury news from Saturday night's game, left fielder David DeJesus left in the second with soreness in his right ankle. DeJesus was replaced at the top of the lineup by Willie Bloomquist, who moved to right field. Mitch Maier then slid over to fill DeJesus' spot in left field.
DeJesus saw his career-high 17-game hitting streak snapped after he struck out swinging in his only at-bat in the top of the first inning.
"We probably saw it on the first AB on the strikeout," Hillman said of the injury. "It was sore. He's not sure what he did to it. It's just sore. He's going to be day to day."
Royals catcher Miguel Olivo also exited prematurely in the third, due to a stomach disorder. He was replaced by John Buck. Olivo walked and scored a run in the second, one night after establishing a career high with six RBIs in an 11-0 victory against the White Sox.
Olivo blamed his stomach ailment on seafood that he ate earlier in the day.
"When I was hitting [in pregame], I started throwing up," Olivo said. "When I went to the bullpen I started feeling sick again, throw up again. In the second inning, I felt like all my strength went away. I said I didn't feel right. My whole body feels weak and Trey comes to me and tells me, 'Let me know,' and I tried to go out for the third inning and started throwing up again.
"I just came out of the game. I don't like to come out, but at that moment I needed to do it because I felt I didn't have any power."