Bruce Springsteen is finally slowing down after more than 50 years of relentless touring — and sources exclusively tell Closer mounting health problems now threaten to silence one of rock ‘n’ roll’s most powerful voices.

Just months after the Boss was forced to cancel a slew of U.S. concert dates due to a crippling peptic ulcer, the 74-year-old rocker axed a string of European shows in late May and early June for what his management called “vocal issues.”

In his storied career, Bruce has played more than 3,500 concerts, marathon affairs lasting between three and four hours. But now fans across the globe fear the canceled shows may signal the end of his touring glory days.

“Bruce is America’s biggest musical road warrior,” declares an insider. “He always told his pals he was going to be up on stage giving his all into his 80s, but the wear and tear on his voice along with other health issues have even Bruce fearing his days as a performer are numbered.”

Last fall, the “Dancing in the Dark” hitmaker faced the grim notion he might never sing again because of the pain caused by his peptic ulcer. “You sing with your diaphragm,” Springsteen explained. “You know, my diaphragm was hurting so badly that when I went to make the effort to sing, it was killing me, so I literally couldn’t sing at all. You’re thinking, am I ever going to sing again?”

Sources say doctors managed to get that medical issue under control with antibiotics and diet, but Bruce is fighting an uphill battle to complete the current tour with his E Street Band.

“The biggest problem is that his ulcer pain can flare up at any time and he’s got to pull back and address it,” reveals the insider. “It just guts him to have to disappoint a stadium crowd by canceling a show right under their noses. Bruce comes from a working-class home and he knows fans take time off work, hire babysitters and book hotels to see his shows. I think he’s at the point where he would rather just hang it up than let down his fans.”

Bruce apparently has had long heart-to-hearts about his musical future with Patti Scialfa, his wife of 33 years who also sings in the band.

“He asks Patti, ‘Have I hung around too long?'” confides the insider. “He’s at the crossroads now. He feels his body and his singing voice breaking down, and it’s robbing him of what he feels he was meant to do — entertain the crowd!”