The author of a book about AC/DC's Young brothers says mainman Malcolm won't return to the band due to his health problems.

Jesse Fink insists fans who have been hoping the 61-year-old's absence was temporary will have to get used to the fact that it's permanent, and that his nephew Stevie, who appears on their upcoming album, is the man they'll see on the road in his place.

The Aussie giants have remained tight-lipped about Young's condition in order to protect his privacy. The only official statement announced he'd be "taking a break" while his colleagues worked on the follow-up to 2008's Black Ice. No one has commented on speculation that he's suffered a stroke, has cancer or is fighting Alzheimer's disease.

Fink also refuses to discuss specifics – but he tells WZLX: "I'm not expecting to see Malcolm return. The important thing is we all let Mal be and hope he can recover. We should all expect that Stevie is in the band now."

He tells British Ultimate Classic Rock: "Fans seem to think his illness is going to go away, and he's going to be on stage when they announce their tour. If what I've heard from numerous sources is true, I expect Stevie will be touring with the band, and not Malcolm. That's not a seditious viewpoint – it's realistic."

He adds that he's received positive reports about the album, which was completed last month. "I'm hearing on very reliable authority it's up there with Black Ice, or even better," the author says. "So Stevie must be a good replacement for Mal."

Frontman Brian Johnson said in June that AC/DC were aiming to be back on the road before the end of the year.

Fink's book The Youngs: The Brothers Who Built AC/DC is published in the UK in October.