Strathmartine Hospital could be on its “last legs” after a fire ravaged the building this week.
Angus Council is still assessing the extent of the damage, caused by a blaze that is believed to have been started deliberately on Monday night.
Local conservation campaigner Karen McCauley, who managed the Strathmartine Hospital Histories project, said she fears the incident could signal the death-knell for the listed building.
The former hospital for people with learning disabilities has been targeted repeatedly by vandals and fireraisers.
The site is currently up for sale with plans to redevelop it into housing.
Karen said: “From a safety perspective, it has got to the point where the building may have to be taken down to just one level.
“I don’t know how much longer the building will hold up. It could be on its last legs after this latest incident.”
It took firefighters more than two hours to extinguish the latest blaze and police are investigating the circumstances.
The hospital was sold by NHS Tayside in May 2005 and is now owned by Heathfield Ltd.