Armstrong is set to undergo treatment for substance abuse, a spokesperson for the group has confirmed. The band has also postponed several upcoming promotional appearances, reported Ace Showbiz.
"'Green Day' wants to apologise to those they offended at the 'iHeartRadio Festival' in Las Vegas. The band regretfully must postpone some of their upcoming promotional appearances," the spokesperson said.
The group's frontman had a very public meltdown on stage in Las Vegas over the weekend, where the group was performing at the star-studded 'iHeartRadio Music Festival'.
The 40-year-old singer was videotaped screaming profanities and slamming Justin Bieber during the band's performance at the annual three-day festival before violently smashing his guitar on-stage, complaining their performance had been cut short.
Armstrong was hospitalised in Italy earlier this month for an undisclosed ailment but recovered in time for his band to perform at the 'MTV Video Music Awards' on September 6.
'Green Day' will release their new album 'Uno' this week and is due to kick off a new US tour on November 26 in Seattle.