The second baseman, a 12-year veteran with 252 homers, was designated for assignment. Seattle has 10 days to trade him or put him on waivers.
"It's tough. I was looking at it, and I think it's all for the better, really. I think it's time for me to go," Boone said, his voice breaking up. "It's still emotional. I'm actually excited about what the future holds but ... It's a pretty sad day for me."
Boone, 36, is hitting .231 with seven homers and 34 RBI. He was benched for four games two weeks ago to work on his swing with batting instructor Don Baylor. On his return, he played well during a three-game series in San Diego, but manager Mike Hargrove said Sunday that "he has reverted back to where he was before."
Seattle is responsible for the remainder of his $8.25 million salary this year. Boone talked to his teammates after the game and then spoke with reporters.
"There was no anger. It was kind of sad," Boone said. "Once it happened, I went home. I just wanted to collect myself and watch and think about what happened. I want to go get a fresh start somewhere. I want to win."
He added that he wants to go to a team where he'll be an everyday player.
"I'm very disappointed on how I've played to this point," Boone said. "Sometimes change is good. It lights a spark and you get back to being more like yourself. It's just time."
General manager Bill Bavasi said the 10-day period to deal with Boone "was to put a deadline on ourselves as well as anyone who has interest in him."
"People mistake designating a player as a loss of leverage," Bavasi said. "You have to evaluate the leverage you had. A deadline applies some sort of leverage. I don't want to say we are hopeful of making a deal that significantly improves this club. Our goal right now is to make as fair a deal as we can make and find a place where he can play every day."
Bavasi said that he had talked to several clubs about potential trades involving Boone. He said he had the makings of a deal a week ago "but it didn't have legs."
"We had some decent discussions but as you know very little happens in baseball without a deadline," he said. "We felt a change was in order. We want to get better every day. We want to improve our club right now. It's as much as getting Jose Lopez on the club as it was to designate Bret Boone for assignment."
Bavasi said that Boone was "very, very professional" when told the news two hours before Sunday's 2-1 win over Texas. Boone's father, Bob, and grandfather, Ray, were both major-leaguers.
"He understands the business," Bavasi said. "That's not to say he was happy about it. He likes Seattle. He has had a lot of good times here. So it's difficult."
Lopez was hitting .264 with four home runs and 11 RBI for Tacoma. He had missed the first six weeks of the season after surgery to repair a broken bone in his left hand. While Boone was benched, Lopez played second for the Mariners and hit .250 with a pair of doubles and four RBI in six games. He was sent back to Tacoma after Boone returned to the starting role.