Green Day fans will be saddened to hear that frontman Billie Joe Armstrong might remain in rehab until next year - according to his record label boss Rob Cavallo.

"He's under medical supervision for a while to get him clean. His doctors are still evaluating. All I can say is I don't know if we'll see him before or after Christmas. It's basically undetermined when he will be back," Cavallo told Rolling Stone.

The rock star entered rehab at the end of last month after he had a meltdown at the iHeartRadio festival in Las Vegas. Some sources close to the singer say that rehab was a long time coming: "Billie Joe has been a loose cannon for a long time. It's gone long past time when he should be getting some serious help."

Green Day bassist Mike Dirnt also revealed in a recent interview that "there were signs of things hitting the fan" prior to the festival incident: "He'd been going through his own struggles… We were there with him, but you can only handle things on your own… At the end of the day, when we got off the road, the most important thing was my friend's life."