Johnson bowed out of the band's Rock or Bust World Tour in March (16) because doctors advised him to stop performing live immediately or risk "total hearing loss."

Brian, 68, reveals the doctors' verdict was "the darkest day of my life" in a new statement, in which he admits he had been aware his partial hearing loss was beginning to compromise the quality of his onstage performance because he couldn't hear the guitars or other musicians.

"In all honesty this was something I could not in good conscience allow," he writes in the statement to Rollingstone.com. "Our fans deserve my performance to be at the highest level, and if for any reason I can’t deliver that level of performance I will not disappoint our fans or embarrass the other members of AC DC...

"I am not a quitter and I like to finish what I start, nevertheless, the doctors made it clear to me and my bandmates that I had no choice but to stop... I tried as best as I could to continue despite the pain and hearing loss but it all became too much to bear and too much to risk."

Doctors have made it clear to Brian that he will not be able to perform at arena or stadium venues or risk ruining his hearing for good, but he is "optimistic" that with medical treatment his hearing will improve and he can go back out on tour.

"I am personally crushed by this development more than anyone could ever imagine," he explains. "The emotional experience I feel now is worse than anything I have ever in my life felt before... I cannot imagine going forward without being part of (AC DC), but for now I have no choice. The one thing for certain is that I will always be with AC DC at every show in spirit, if not in person."

He thanks bandmates Angus Young and Cliff Williams, and fans, and assures them that he is not retiring from the band as he is allowed to work in the studio.

Guns 'N Roses frontman Axl Rose is replacing Brian for 10 shows in Europe between May and June (16). Axl will join the group again for ten U.S. dates, which are yet to be rescheduled.