EXCLUSIVE: Inside Barry Manilow's Brutal Setback — How Cancer-Hit Crooner, 82, is Determined to Sing Again… But His Lungs Won't Let Him

Still-ailing Barry Manilow has postponed his comeback as he struggles to recover from cancer surgery, RadarOnline.com can reveal.

The beloved Copacabana crooner, 82, had a cancerous spot on his left lung removed in December and was working out on a treadmill three times a day.

Despite that, the Grammy winner revealed on social media that he "still couldn't sing more than three songs in a row."

As readers know, Manilow had already postponed his mid-February performances at Westgate Las Vegas and had vowed to kick off a tour at the end of February.

But after a "very depressing visit" with his surgeon, the Mandy singer is rescheduling all shows through March 17.

"Deep down, I wanted to go back, but my body knew what my heart didn't want to admit: I wasn't ready," he said.

"I'm SO, SO sorry I have to reschedule some of these first arena shows. Again."

But he's optimistic that he'll "likely" still perform in Vegas in late March and early April.

However, RadarOnline.com has reported pals have worried Manilow – a longtime smoker who traded in his cigarette habit for vapes about a decade ago – isn't ready to perform.

A source said: "The fact that he didn't need chemo or radiation after surgery feels like a miracle.

"Still, it's a little hard for people to see him throwing himself back into work already. There's a sense that he's pushing himself too hard.

"The problem is, Barry does not do anything by halves. When he performs, he gives absolutely everything, and that's what has his friends a little nervous.

"People close to him wish he'd slow down. They know how physically and emotionally demanding those shows are for him.

"Everyone in his circle is incredibly proud of him, but they want him to take his time and make sure he is truly ready."