"At the end of the day, he's coasting," Sir Elton tells Rolling Stone in its new cover story. "I always say, 'Billy, can't you write another song?' It's either fear or laziness. It upsets me."

The musician clearly takes Joel's problem seriously - and personally. "Billy's a conundrum," John, 63, says of the 61 year-old. "We've had so many canceled tours because of illnesses and various other things, alcoholism."

Addressing Joel's drinking, John says: "He's going to hate me for this, but every time he goes to rehab they've been light. When I went to rehab, I had to clean the floors. He goes to rehab where they have TVs."

Directing his comments to the "Piano Man," the "Rocket Man" says: "I love you, Billy, and this is tough love. Billy, you have your demons and you're not going to get rid of them at rehab light. You've got to be serious. People adore you, they love you and respect you. You should be able to do something better than what you're doing now."

In response to John's remarks, Joel issued a statement. It said, "I've worked with Elton for such a long time and I've enjoyed our relationship too much to let something as random as these comments change my affection for him. Elton is just being Elton."

"When I went to rehab, I had to clean the floors. He goes to rehab where they have TVs. I love you, Billy, and this is tough love."

But in an interview with CNN this week, the singer shrugged off Elton's comments. "I've worked with Elton for such a long time and I've enjoyed our relationship too much to let something as random as these comments change my affection for him," he said.

Joel added: "Elton is just being Elton."

Indeed, Billy isn't the only star to fall victim to the outspoken icon's harsh tongue. In a separate interview this week, Elton John launched a foul-mouthed tirade on everyone from Kim Kardashian and Cheryl Cole to The Saturdays, and Westlife.

"Frankly, they all sound the same," he said. "It's hard to tell Girls Aloud from The Saturdays. And then there's Cheryl Cole...it's all crap."

He told magazine The Word: "British pop music like that is the worst, it's just awful, it could have been made by anybody." John went on to speak out against lip-synchers, saying that they "should be shot" - before launching into a tirade against boy bands.

"Go and see Take That or Westlife," he said, "and how much of that is live?" "I know Gary Barlow can sing live, that solves that one. I think they genuinely do sing their stuff, but 99% of the other fucking Herberts out there can't sing a note." He added: "Who the fuck is Kim Kardashian?" he asked. "Some stupid old tart from somewhere. Reality has killed talent." The 63 year-old also criticized Billy Joel's "lazy" approach to his career.

"At the end of the day, he's coasting," John, who has freely spoken about his own past issues with substance abuse, tells the magazine. "I always say, 'Billy, can't you write another song?'" It's either fear or laziness. It upsets me. Billy's a conundrum. We've had so many canceled tours because of illnesses and various other things, alcoholism.'

Joel spent a month in a California rehab center for treatment of alcohol abuse in 2005. He spent about two weeks at a Connecticut facility in 2002.