"I don't think it's anything major. Very minor," Royals manager Ned Yost said.
It's considered a precautionary move to prevent Paulino from risking injury to his elbow or shoulder by adjusting his delivery to compensate for his back discomfort.
Kansas City head athletic trainer Nick Kenney said Paulino's setback is not expected to be a long-term situation. He's cleared to continue throwing, but not in game-type situations.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.