Cain was competing for a fifth outfield spot with Jarrod Dyson and Gregor Blanco but manager Ned Yost didn't want him parked on the bench for Kansas City.
"I've always found that there's a player every now and then -- Kila [Ka'aihue] was one last year, when I took this job -- that makes me real uncomfortable sitting on my bench because he's a special player. He has the ability to be an everyday player, a young player that needs the at-bats," Yost said.
"Has Lorenzo Cain played well enough to make this club? Sure he has. But, for me, I don't rest well knowing I have a kid like Lorenzo on my team playing once or twice a week. I want Lorenzo playing six and seven times a week down there so that when we get to the point where he comes back up here, we can pencil him in the lineup every single day."
Cain batted .289 (11-for-38) in 18 Cactus League games with three doubles, three RBIs and three stolen bases. He also made spectacular catches in center field.
But the Royals are committed to using Melky Cabrera, the American League's top hitter in Spring Training, in center field, with Alex Gordon in left and Jeff Francoeur in right. Mitch Maier is the fourth outfielder.
"You can make a case for having Cain on your team because he makes your team better," Yost said. "But he's going to be here when we win a World Series and he'll be in center field or right field or wherever he's going to be. He'll be manning that spot and be a very productive part of that team and helping us get there. So I can't, in good conscience, let him come with us and sit the bench."
Cain, 24, a right-handed hitter, arrived during the winter in the six-player Zack Greinke trade with the Milwaukee Brewers. Last season, Cain played in 43 Major League games and hit .306 with a home run, 13 RBIs and seven stolen bases in eight tries for the Brewers.
He was in the Brewers' system for six years after being a 17th-round draft choice in 2004 out of Madison, Fla. He didn't play organized baseball until he was a sophomore in high school.
The departure of Cain, pitcher Robert Fish and third baseman Pedro Feliz on Sunday leaves the Royals with six cuts to make to get down to the 25-man Opening Day roster. There are 34 players still in camp, but that includes two rehabbing players, catcher Jason Kendall and pitcher Zach Miner, and one on the 60-day disabled list, pitcher Henry Barrera.
One cut will be starting pitcher Vin Mazzaro, who will be optioned to a Minor League team for a couple of weeks until he's needed on April 16.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.