Nomo, 39, was attempting to come back from elbow surgery and defied the odds by making the Royals' roster. But he was largely ineffective and was hit hard in his last appearance on Friday night against Oakland.
Royals manager Trey Hillman gave Nomo the news after Saturday's game against the A's and made the announcement on Sunday morning.
"I told him how much we appreciated his efforts and his energy that he brings in a very quiet and humble way," Hillman said. "He's the kind of a guy that makes people better being around without saying anything because he's so professional and because of what he's done as a Major League player here in the United States and also what he did in Japan."
Nomo was not available to comment. His agent, Don Nomura, awakened at 2 a.m. in Tokyo, said he wasn't aware of the Royals' decision.
Hillman said Nomo gave no indication if he'd retire or continue pitching.
"He did not and I didn't ask. That would have been really bad timing for me to ask those questions," Hillman said.
Nomo has a 10-day period in which he could be traded or put on waivers. In any event, the Royals will not offer him a spot at Triple-A Omaha.
Until pitching for the Royals, Nomo had not pitched in the Major Leagues since 2005 with Tampa Bay.
Nomo had an 18.69 ERA for the Royals in three games and 4 1/3 innings. On Friday night, he entered the game in relief of countryman Yasuhiko Yabuta and induced a popup for an apparent third out but the ball dropped safely for a two-run double. Then he gave up a single and Bobby Crosby slammed a long home run to center field.
"Unfortunately, the performance level wasn't what we hoped it'd be and the velocity on the fastball wasn't as consistent as it was in Spring Training," Hillman said. "The split is still there, not with the same repetitiveness and to the same degree of depth that we saw in Spring Training. But it's a very short sample during the games he pitched once the season started -- not a very big sample to be able to evaluate it fairly from."
When Nomo was signed last winter, he was viewed as a mentor and companion to Yabuta, a reliever who was making the transition from Japan to the United States. He accomplished that.
"We won't be able to be play together, but this is my first year in the United States and I didn't know my right from my left. But he gave me a lot of advice that meant a lot to me," Yabuta said after learning of Nomo's departure.
"So I really appreciate what he did for me. He was a big help to me."
As Spring Training went on, the hard-working Nomo increased his velocity and his famed split-finger pitch showed signs of old. He abandoned his signature "tornado" windup, in which he turned his back to hitters, and merely pitched out of the stretch to take stress off this elbow.
In seven Cactus League games, he struck out 17 in 15 innings and his ability to "miss bats" impressed Hillman. His ERA was 4.80 with one victory in seven appearances. Late in camp, Nomo was removed from consideration from the starting rotation and competed instead for a bullpen spot.
He was not on the active roster when the season began as he recovered from a groin injury. He was added to the roster when catcher Miguel Olivo's four-game suspension ended on April 5, the roster was restored to 25 men and catcher Matt Tupman was optioned to Omaha.
The latest move was set into motion when starter John Bale was placed on the disabled list. Reliever Joel Peralta was recalled from Omaha to replace Bale but a starter was needed for Sunday's game against Oakland. So Luke Hochevar was recalled and Nomo was cut from the roster.
"It's unfortunate timing but I believe we made the right decision for what we've got to do for our club in trying to move forward and trying to win games right now," Hillman said.
Nomo was a Japanese trailblazer when he left the Kintetsu Buffaloes after a contract dispute and joined the Los Angeles Dodgers in 1995. He was the first Major Leaguer from Japan in 20 years, since Masanori Murakami, and more than 30 would follow him.
"Nomo-mania" soon became part of the baseball lexicon.
With Japan following every move, Nomo won a National League Rookie of the Year trophy, started an All-Star Game, won 123 games, pitched two no-hitters and had 200 strikeouts four times.
Hillman, who managed for five years in Japan, was well aware of Nomo's impact. He called Nomo a "great warrior" and praised him as a quiet leader and a good example for younger players. But for Nomo and the Royals, it was over.
"I have no reservations in saying I wish it had lasted a lot longer," Hillman said.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.