Matt Harvey, whose rapid ascent has been both mesmerizing and polarizing, now faces shoulder surgery that could dim what has been a bright career.

Mets general manager Sandy Alderson said yesterday that a St. Louis-based specialist has diagnosed the righthander with symptoms consistent with thoracic outlet syndrome (TOS), a condition that causes numbness stemming from compressed nerves and blood vessels near the shoulder. Harvey is dealing primarily with a nerve issue.

He ultimately will choose a course of action, a decision that Alderson expects before the All-Star break. Surgery brings with it a four-month rehab, which would knock out Harvey for the rest of the year.

Though alternative methods such as a nerve-blocking injection could delay corrective surgery until the offseason, Alderson called it a “temporary fix.”

“I do believe that surgery is probably inevitable and more a question of timing than anything else,” Alderson said.

Of course, surgery brings uncertainty. Operations to resolve TOS have brought a wide range of outcomes. Some pitchers, such as Josh Beckett and Chris Young, have bounced back and resumed their careers after surgery. But others, such as Jeremy Bonderman and Noah Lowry, were left in a diminished state, their careers effectively over.

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Twins righthander Phil Hughes underwent shoulder surgery to treat TOS this week, though it came nearly five years after he was first suspected of having the condition in 2011 while pitching with the Yankees.

The condition, Alderson said, can be caused by muscle buildup, bone displacement or repetitive use. But he refused to cite Harvey’s heavy 2015 workload — 216 innings, including the postseason — as a possible cause.

The Mets hitched their hopes for a return to the World Series to pitching. Despite Harvey’s struggles this season, his absence would only further weaken a rotation that already has shown signs of erosion.

Steven Matz remains a candidate to undergo season-ending elbow surgery to remove a bone spur. Though doctors have reassured the Mets that pitching through it will not increase the risk of ligament damage, it’s possible that the pain can become too much to handle.

Matt Harvey in the second inning of his start against the Miami Marlins at Citi Field on Monday, July 4, 2016. Photo Credit: Jim McIsaac

Delays in Zack Wheeler’s rehab from Tommy John surgery have left his status up in the air. He had been expected to rejoin the rotation shortly after the All-Star break, but Alderson has lowered those expectations.

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Alderson said he is “confident” that Wheeler will return at some point this season, though also “not certain.”

“Now we have no idea when he’s coming,” manager Terry Collins said.

Harvey, 27, is in the middle of his worst season in the big leagues. A year ago, he was brilliant in his first year after Tommy John surgery, carrying a heavy workload while helping the Mets to the pennant. But this season, he has shown none of that dominance. He is 4-10 with a 4.86 ERA, and at his nadir, that figure had rocketed above 6.

Early in the season, Harvey struggled to regain the velocity and explosiveness on his fastball. And even as he showed signs of emerging from his funk, they proved to be fleeting.

Through it all, both Harvey and the Mets insisted that health was not a factor.

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It’s unclear when he began experiencing symptoms from TOS. But after his last start, a lackluster six-run effort against the Marlins on Monday, Collins said he complained of several disturbing symptoms.

“He came into the training room afterward and said ‘my shoulder’s dead, my arm’s dead, there’s no energy there, I couldn’t feel the ball,’ ” Collins said.

All are associated with TOS, which is why team doctors referred Harvey to Dr. Robert Thompson, considered one of the world’s top specialists.

His next start was scheduled for tomorrow against the Nationals. But with Harvey on the 15-day disabled list, righty Logan Verrett will take the assignment.