Matt Harvey of the Mets walks to the dugout after...

Matt Harvey of the Mets walks to the dugout after an inning against the Braves at Citi Field on Thursday. Credit: Jim McIsaac

General manager Sandy Alderson said the Mets will designate Matt Harvey for assignment Saturday after the onetime ace refused to accept an assignment to the minors.

Harvey started the season in the rotation but struggled and was demoted to the bullpen two weeks ago.

“It’s the end of an era,” Alderson said. “I use that term in a broad sense. Matt has been a cornerstone of certainly my tenure here. Tremendous prospect at the time when I arrived. Tremendous accomplishments during the course of my tenure here.”

Alderson, assistant GM John Ricco, manager Mickey Callaway and pitching coach Dave Eiland met with Harvey at about 3:15 p.m. Friday. Alderson said they told Harvey they thought he would benefit from some time at the team’s minor-league complex in Port St. Lucie, Florida. They offered Harvey a few hours to mull it over and speak with his agent, Scott Boras.

Harvey, 29, apparently didn’t need much time. Alderson announced the move at 4 p.m. The Mets will have seven days to trade or release Harvey.

Reached Friday night, Boras said in a text: “We feel Matt is a starter needs to work on 4 pitches. In the bullpen a pitcher tends to focus on 2 pitches to get back to the rotation . . . Very pleased he is healthy and with more than needed MLB velo. we have a lot of clay to work with to build the starter sculpture.”

Harvey was not available to reporters.

“This was a long time coming,” Alderson said. “This is not someone who hasn’t pitched well recently. This is something we’ve tried to address, we’ve struggled with, we’ve wrestled with over two managerial regimes. The move to the bullpen was dramatic in itself. At this point, pragmatism, realism far outweighed other considerations.”

Harvey’s struggles reached new depths this year. He lost his rotation spot with an 0-2 record and a 6.00 ERA. In four games in relief, he allowed seven runs in six innings; the Braves scored five runs in two innings against Harvey on Thursday. Opposing batters had a .303/.355/.550 slash line against him this season.

“There’s ways to help guys in the bullpen from the way they attack and the mentality that you have to have out of the bullpen,” Callaway said. “It became obvious that maybe that wasn’t the case with Matt. There were some mechanical issues that also needed to be addressed. And that’s tough to do in a major-league game.”

Harvey labored through the worst year of his career in 2017 (6.70 ERA, 1.69 WHIP), He went 5-7 in 19 games, missing time with a stress fracture in his scapula.

The Mets believed two weeks ago that the bullpen would be the best spot for Harvey to straighten himself out. Callaway cited his and Eiland’s starter-in-the-bullpen success stories with previous teams as evidence.

“We feel like we failed Matt Harvey,” Callaway said. “Our job is to help every player in there. It’s not a good feeling when we can’t.”

Harvey’s Mets career paired high peaks with deep lows. He went 12-10 with a 2.39 ERA and 261 strikeouts in his first two seasons in 2012-13, earning the start for the 2013 All-Star Game at Citi Field. He finished fourth in the 2013 NL Cy Young Award voting. But he then had Tommy John surgery and missed the entire 2014 season.

Harvey came back in 2015 and made 29 starts, finishing 13-8 with a 2.71 ERA and 188 strikeouts as the Mets reached the World Series. But after struggling during the 2016 season (4-10, 4.86 ERA in 17 starts), he was diagnosed with thoracic outlet syndrome and had season-ending surgery.

Harvey also was the subject of several off-field incidents. Most notably, he was suspended for three games in May 2017 after not showing up for a game.

The Mets will try to work out a trade. If they can’t, Harvey will become a free agent.

“My guess is that there are people out there who are willing to take a shot on Matt Harvey,” Alderson said. “We’ll see.”

Harvey had a minor-league option left, but with more than five years of major-league service, he had to approve the demotion.

Alderson said he couldn’t get into why Harvey wouldn’t accept the assignment. “There wasn’t a lot of discussion,” he said. “I can’t get inside of Matt’s decision. I could speculate, which I’m not prepared to do here. But he didn’t really express any rationale.”

Said Callaway: “He just didn’t feel that was the right spot for him to continue to be the player he wants to be.”

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