Billie Joe Armstrong has been a "loose cannon" for a long time, it has been claimed.

The Green Day frontman was allegedly showing signs he needed professional help long before his reported breakdown on Friday. Billie Joe burst into an expletive-laced rant that included a steady stream of the f-word on stage during his performance at the iHeartRadio festival.

Following his shocking outburst Billie Joe announced he would be undergoing treatment for substance abuse on Sunday. However, sources close to the singer say he should have been admitted to rehab long before his on-stage breakdown took place.

"Billie Joe has been a loose cannon for a long time," a Green Day insider told the Chicago Sun-Times. "It's gone long past time when he should be getting some serious help."

Billie Joe's foul-mouthed rant was caused by him being told that the band needed to wrap up their set during the festival performance.

"You're going to give me one minute? One f**king minute? I've been around since f**king 19 f**king 80 f**king 8, and you're going to give me one f**king minute?" Billie Joe ranted. "I'm not f**king Justin Bieber, you motherf**kers."

Billie Joe then stormed off stage, smashing his guitar as he exited. The band later issued a statement apologising for the incident.

Signs indicated there was trouble brewing for Billie Joe's health when he was rushed to hospital earlier this month. This forced Green Day to cancel a concert they were scheduled to play in Italy.

At the time it was reported the reason for his hospital admittance was "severe dehydration", although now it appears hard-partying could have been the real cause of the cancellation.