The 49-year-old Moyer said in a news conference Wednesday that he still had hopes of continuing his career elsewhere but his immediate plan was to return home and attend a son's high school graduation.
"It's a tough pill to swallow but it's part of the business," Moyer said.
Rockies manager Jim Tracy told Moyer of the team's decision in a meeting earlier Wednesday. The Rockies recalled Carlos Torres from Triple-A Colorado Springs to take Moyers' roster spot.
After missing all of the 2011 season while recovering from reconstructive elbow surgery, Moyer signed with the Rockies and made the team with an impressive spring training. He became the oldest pitcher to win as a starter on April 17, when he led the Rockies to a 5-3 win over the San Diego Padres.
"I enjoyed my time here in Denver," Moyer said, expressing his appreciation both to Rockies general manager Dan O'Dowd and Tracy for helping him to revive his career after a year away from the game.
"Dan gave me a great opportunity in spring training. Jim stuck his neck out for me. He gave me an opportunity and that's all I can ask for, when I came, an opportunity," Moyer added.. "Unfortunately I didn't hold up to my end of the bargain. That's what happens in the game."
Moyer had struggled recently. He was 2-5 with a 5.70 ERA in 10 starts. By designating him for assignment the Rockies have 10 days to trade him or release him.
"I just felt like that by sending him out there, we were compromising him and the team," Tracy said before Wednesday night's game against the Houston Astros. "It's difficult, because he's as professional as any player I've ever been around. But we felt like this is something we had to do."
Moyer picked up his second win of the season a month after his milestone victory, allowing one earned run and six hits in 6 1-3 innings in the Rockies' 6-1 win over the Arizona Diamondbacks on May 16.
But the successes were proving few and far between. In his last start at Cincinnati on Sunday, Moyer was unable to hold a 5-0 lead and took the loss in a 7-5 Rockies' setback. He went five innings and gave up seven hits and seven runs.
"It is all about putting up results, individually and as a team," Moyer said. "When you don't do that, obviously management has to just step back and reevaluate things and their choices are their decisions."
When asked, though, if he thought he could still pitch, Moyer said, "I do believe so."
He added that he thought he could iron out his problems with his command and consistency.
"When you talk to any pitchers, consistency is the most important thing," Moyer said. "I haven't had that to this point. But I know I can find that."
Over the course of his 24-year career, Moyer has gone 269-209 with a 4.25 ERA while playing for eight big league teams. Moyer also has pitched for Philadelphia (2010-2006), Seattle (2006-1997), Boston (1996), Baltimore (1995-1993), St. Louis (1991), Texas (191990-1989) and the Chicago Cubs (1988-86).