According to a report by The Associated Press, several Royals stepped in to separate Guillen and McClure after some chairs were knocked over during the heated argument.
Guillen was sitting at a table by his locker when he toppled over a chair and made a comment in Spanish, the AP said. After a teammate attempted to calm him down, Guillen grew more agitated, tossed over another chair and said, "Coaches don't need to be all up in our ... business."
McClure, who was sitting at his locker, exchanged words with Guillen from across the locker room before Guillen tossed over another chair and got in the pitching coach's face.
Hillman was in the dugout talking with the media when the altercation took place, but was seen speaking with Guillen prior to batting practice.
Following Saturday night's game, Hillman dismissed the incident and said it was "absolutely" over.
"It's been handled in-house and will remain in-house," he said, adding that he would not characterize the incident. "Honestly, it's not an issue."
Hillman declined to comment on whether Guillen would face any repercussions and said that the pregame spat did not have any carry-over into Saturday night's loss.
This isn't the first flare-up from Guillen. The outfielder sounded off in a profanity-laden tirade in May about his Royals teammates, calling them "babies" after a Kansas City loss.
Guillen made his scheduled start in right field on Saturday night, going 0-for-4 in the loss. Both Guillen and McClure declined to address the incident with the media.
Brittany Ghiroli is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.