Tre Cool, Billie Joe Armstrong, Mike Dirnt of Green Day. (WENN.com)

Green Day star Mike Dirnt has opened up about the health crisis which sent frontman Billie Joe Armstrong to rehab, revealing the singer was overworked and tired when he suffered a meltdown at a show in Las Vegas.

The 21 Guns star checked himself into a treatment facility the following day for substance abuse issues, and now his bandmate has shed a little light on what went wrong.

Bass player Dirnt tells BBC Radio 1 Armstrong was under a lot of pressure as the group embarked on a major campaign to promote three albums in four months.

He says, "It was a tremendous undertaking... (and) it catches up with you a little bit. We definitely jumped off a moving train.

"All that inertia. There were signs of things hitting the fan, we hadn't slept in forever."

Dirnt admits he hasn't seen Armstrong since the Las Vegas meltdown, when Armstrong hurled expletives at the organisers of the iHeartRadio Music Festival for trying to cut his set.

But the rocker insists he and fellow bandmate Tre Cool had no qualms about scrapping their promotional commitments as Armstrong sought help, adding, "We had to put the life of our friend in front of everything."

Armstrong appeared on TV talent show The Voice on Monday in a segment that was taped before his meltdown and subsequent rehab stint, which is ongoing.

As his debut on The Voice aired, the band announced plans to pull its appearance at this month's Voodoo Music + Arts Experience in New Orleans, Louisiana.

Drummer Cool tells WENN, "Cancelling shows is something we rarely do. We never want to let our fans down, and we are grateful for all of you being understanding during this time."