Schuster, 23, was placed on the Royals' 40-man roster, and outfielder Carlos Peguero was designated for assignment to make room.
A reliever, Schuster was selected by the Astros from the Diamondbacks in last December's Rule 5 Draft and then traded to the Padres for pitcher Anthony Bass.
Because Schuster falls under Rule 5, if he's still on the 40-man roster by Opening Day the Royals would be obligated to keep him on the 25-man active roster for the entire season or offer him back to the Diamondbacks. Keeping him on the active roster is an unlikely event so the Royals could negotiate a deal with the Diamondbacks to negate the Rule 5 obligation and send him to the Minors.
"We got him for depth, we'll go from there, see what happens the next couple of days," manager Ned Yost said.
Schuster, who has not pitched above the Class A level, had a 1.83 ERA in 55 games last year for Visalia in the Diamondbacks' system. Considered a situational lefty, he had 45 strikeouts and gave up 30 hits and 18 walks in 44 1/3 innings.
Peguero, 27, was claimed off waivers by the Royals from the Mariners in January. The 6-foot-5 left-handed batter had a good camp, hitting .313 (10-for-32) with two homers and eight RBIs, but there was no spot for him with Jarrod Dyson and Justin Maxwell holding the two backup outfield spots.
Moore, 29, was cut by the Royals on Monday and reassigned to the Minor League camp. Considered a good defensive catcher, he hit just .167 (3-for-18) in Cactus League games.
Last year, Moore spent one week with Kansas City while regular Salvador Perez was on the bereavement list. In five games, he was 3-for-10. In 2012, he was a September callup from Triple-A Omaha and homered in his first at-bat.
Previously, Moore played in the Majors with the Mariners -- a total of 68 games, including 58 starts in 2010. His career average for 77 big league games is .200.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.