In a statement on their website the band said any rescheduled gigs will “be made up later this year, likely with a guest vocalist.”
Doctors have reportedly advised Johnson to stop touring immediately.
Fans have now been left in doubt as to whether the long-running Australian hard rock band will be playing the European leg of their ‘Rock Or Bust’ tour, which is due to begin on 7 May in Lisbon on the Passeio Marítimo de Algés.
More than 29,000 tickets have been sold for the Lisbon concert.
The Portugal News approached the band’s Portugal concert promoters ‘Everything Is New’ for comment but none had been received by the time of going to press.