De La Rosa got the word on Wednesday morning.
"This is the first time this has happened to me, and I'm a little bit surprised," De La Rosa said. "It's tough, but I've got to be better."
The Royals also obtained right-handed reliever Ramon Ramirez in a trade with the Rockies for a player to be named.
In addition, the Royals reassigned right-hander Chin-hui Tsao to Triple-A Omaha and right-hander Roman Colon to Double-A Northwest Arkansas. Both will be in the bullpen for those clubs.
In other moves, the Royals traded outfielder Justin Huber to the Padres for a player to be named, released non-roster pitcher Brian Lawrence and reassigned non-roster catcher Ken Huckaby to the Minor League camp.
Lawrence, who was a non-roster pitcher in the Major League camp, had been reassigned to the Minors. However, the Royals didn't see a spot for him in the Omaha rotation.
De La Rosa, who'll turn 27 on April 5, will go on waivers. If he clears, he can become a free agent. It's also possible the organization could offer him a spot at Omaha, and Royals manager Trey Hillman said that has been discussed.
De La Rosa began the 2007 season in the rotation and started out well with a 4-3 record and 3.59 ERA in his first nine starts. Later he struggled, went on the disabled list on Aug. 1 with a sore elbow and finished the season in relief.
His final mark was 8-12 with a 5.82 ERA. After being acquired from the Brewers on July 25, 2006, for infielder Tony Graffanino, the lefty was 11-16 and had a 5.64 ERA in 36 games for the Royals.
This spring, De La Rosa was up and down, but he finished four Cactus League outings with an 8.03 ERA, 10 strikeouts, eight walks and three home runs in 12 1/3 innings. His lack of command has been a constant battle for him.
"My arm feels very good -- it feels strong," he said. "Just my command -- I've got to work on that and try to do something."
As recently as Tuesday, Hillman noted that De La Rosa had "electric stuff."
"He didn't say that today," De La Rosa said after his meeting with the manager.
Davies will be in the Omaha rotation. In spring games, he pitched just nine innings and had a 4.00 ERA. The Royals liked his stuff, but they said he needs more consistency in his delivery.
The Royals also announced that right-hander Luke Hudson, who is coming off shoulder surgery, will remain in Arizona for extended Spring Training. Hudson hasn't been pitching, and he is five or six days away from resuming throwing, Hillman said.
There's still no word from the Commissioner's Office about the suspension appeals of right fielder Jose Guillen and catcher Miguel Olivo. Because of Olivo's five-game suspension, the Royals would have to begin the season with just 24 players.
"It could get reduced, but I don't think it'll get reversed," Kansas City general manager Dayton Moore said.