Preston's Guild Hall has suffered a fresh setback to its re-opening over fears it has crumbling concrete issues, the city council said.
The Grand Hall and Charter Theatre will be secured while specialist structural engineers investigate if it "is present in the roof panels".
Both venues have been closed since 2019 but they were due to open soon.
Schools and other buildings have been closed after reinforced autoclaved aerated concrete (Raac) was found.
Several theatres have also been closed over safety fears.
Preston City Council said "it is believed" Raac is present in the roof.
A spokesperson said: "We are taking a cautious and 'safety first' approach by securing the Grand Hall and Charter Theatre auditoria, until specialist consultant structural engineers can carry out a more detailed inspection.
"Unfortunately, we understand that this may take some time, as the experts required to carry out this very particular type of work are naturally prioritising school inspections."
Ground floor trading units and the Harris Library remain open inside the building.
The Guild Hall and Charter Theatre opened in 1973.
Over the years, it hosted major snooker events and the likes of Queen and David Bowie performed there but it was shut in May 2019.