Staff at the Pavilion Theatre will not be allowed access to the building for about two months after a major fire in Glasgow city centre.
The blaze broke out about 08:20 last Thursday and devastated a block, which included Victoria's nightclub.
On Monday, Glasgow City Council confirmed the buildings were unsafe and will have to be pulled down.
More than 120 firefighters prevented the flames from spreading to the neighbouring 114-year-old Pavilion.
But it will be weeks before the historic theatre can return to normal.
A statement issued on Monday night said: "This is indeed the saddest day we have had since the flood in 1992.
"After waiting to hear all day, we have just been advised by Glasgow City Council Building Control that we will be denied access to the theatre for around two months.
"After which, we will then be allowed in to ascertain the damage caused by the fire.
"Only then will we be able to carry out any works required."
The statement confirmed staff had requested access to the building last week but were denied.
It concluded: "We will issue a further update regarding the shows tomorrow in more detail as we have a lot to think about just now, either moving shows to other venues or rescheduling these to later in the year.
"We hope you can bear with us on this as it has taken us by surprise and intend to seek the help of senior personnel in the council and perhaps the Scottish government as surely there are ways around this.
"Again, we would like to thank everybody for their continual support of the theatre and we hope to give you more information as soon as we can."
Pavilion manager Iain Gordon told the BBC's Good Morning Scotland radio programme he was allowed access to the building briefly to collect some belongings.
He described the interior as "very smelly" due to the smoke and said some doors had been damaged by firefighters in order to get access to the roof during the height of the blaze.
Mr Gordon also confirmed Celtic - The Musical, which had been scheduled to run from 18 April to 12 May, will be moved to September.
Meanwhile, Rumours of Fleetwood Mac on 3 April will be moved to the nearby Glasgow Royal Concert Hall.