"This is probably the best thing for both Carlos and the Cubs," Marmol's agent, Paul Kinzer, told ESPNChicago.com's Bruce Levine. "But Carlos hates leaving Chicago. He's loved his time there, having been in the organization his entire career.
"I had another player who was designated for assignment a couple years ago, and that was Edwin Encarnacion, and now he's an MVP candidate."
Cubs general manager Jed Hoyer said the Cubs gave up long ago on being able to trade Marmol.
"We realized maybe in August last year that we would never be able to trade him," Hoyer said. "He had a really good second half last year on paper and no one really bid at the deadline. We never really had any offers except for someone else's undesirable contract."
The Cubs also announced the suspension of Ian Stewart was settled and upheld, and he was unconditionally released.
The 30-year-old Marmol went 2-4 with a 5.86 ERA in 31 relief appearances this season. Marmol has struggled for parts of the past three seasons. He struck out 32 and walked 21 in 27 2/3 innings this season. He had 10 blown saves with a 4.01 ERA in 2011 and has lost his closer role on several occasions.
"He had struggles that frustrated people at the end of a game," Hoyer said. "We held out on this move for a long time. Partially because of the salary and that he was providing solid innings. The decision came down to that he had become a distraction. Every time he threw two balls to the first hitter, he was getting booed. It became difficult for his teammates because it had become a bit of a sideshow mentality to it. We just felt it was the right time."
"God gives us the opportunity, and he can take it away; that's the way the things are. This is only business," Marmol said to Enrique Rojas of ESPNdeportes.com via phone from Milwaukee. "You never expect this kind of news. I believe that fans were getting a little strong to me. I think it was time to move and try a new beginning."
Marmol will stay around Chicago and work out and prepare for whatever happens next, Kinzer said.
Marmol, making $9.8 million this season, will be in baseball limbo for 10 days while the Cubs try to work out a trade. After that, he can be asked to take a designation to the minors if he clears waivers. Otherwise, he can opt for free agency. A team will be able to sign him to the minimum salary, while the Cubs will have to absorb the rest of his contract.
"Every time I go to the mound I try to give 100 percent, all I got. I didn't fail for lack of effort. I would say that the lack of support from the fans was part of the reason of the mental block that I suffered recently," Marmol said.
Marmol said that another possible reason for his poor performance is his absence from winter ball in the Dominican Republic over the past three years.
"I need to throw a lot. I'm a pitcher that needs to work a lot to keep his rhythm," Marmol said.
Cubs outfielder Alfonso Soriano, himself the target of boos at Wrigley Field, said it's tough when the home crowd boos gets on one of their own.
"It is very tough when the home fans boo you," Soriano said. "It becomes tougher if you think about it. You just have to block it out and do your job. I have been through it and you can't worry about the fans. They can do what they want. They pay for a ticket. They can do what they want to. We can't pay any attention to that."
Marmol has 117 saves over eight seasons with the Cubs. His best season as a closer came in 2010 when he had 38 saves, a 2.55 ERA and 138 strikeouts in 77 2/3 innings.
"He had a really good career here. He gave a lot to the Cubs and had a really great Cubs career. People would do well to look at his Baseball Reference page and remember how good he was."
The Cubs selected the contract of outfielder Brian Bogusevic.
Stewart was serving a 10-game suspension without pay for violating the loyalty clause in his contract. The 10-game suspension was handed down after he ranted on Twitter about his status within the organization. Stewart, 28, was traded to the Cubs in 2011 and re-signed with the team this offseason. He was hitting .201 and has struggled staying healthy.