A report by architect Tim Ronalds has found that the Old Vic is in "urgent" need of repairs to fix structural problems including a leaky roof.
Temporary asbestos roofing installed after the Second World War has never been replaced.
Ronalds, who worked on the renovation of the Hackney Empire, believes that £13 million will be required to deal with the problems.
The Old Vic Theatre Trust is seeking funding from the Heritage Lottery Fund.
Last month Old Vic chief executive Sally Greene told MPs on the Culture, Media and Sport select committee that the fabric of the Waterloo theatre is in a perilous state: "The roof is letting in water, literally it is dripping onto the set and we need help for the fabric, because we can put on the shows and we can raise the money for the shows but we cannot look after the building at the same time. We are spending a lot of our money at the moment on trying to keep the building going, bit by bit. I cannot remember which production it was but it rained upon what we were doing. This is where we need help."
"We are in a desperate situation because we have a big hole in the roof. I cannot remember exactly which year it was, I think it was in 1941, the Germans bombed London and one of the bombs happened to go through the roof of the Old Vic and it has never been repaired properly. It is really serious now."
There were lighter moments during the committee proceedings. Labour MP Chris Bryant shared some of his own memories of the Old Vic: "My own experience of going to the Old Vic is of sitting through a four-hour production of Hamlet with no interval, with a seat which collapsed after about ten minutes." He went on to recall another occasion when he fell down a staircase at the Old Vic after a meeting with Sir Peter Hall.