Kansas City announced the moves before opening a three-game series against the Oakland Athletics on Friday night.
The 24-year-old Fuentes was acquired from San Diego last November for minor league pitcher Kyle Bartsch. He was 8 for 18 with a double in his first six games in Omaha.
The Royals were seeking a little more offensive production after losing outfielder Alex Rios to a broken finger. Gore was called up to replace him, but he is known primarily for his speed and not his production. He didn't appear in a game while with the Royals.