Part of the Sherwood Forest visitor centre has been closed off after cracks appeared on an ancient oak tree.
Park ranger David Wright said about a third of the centre has been cordoned off due to safety reasons.
A report will be sent to English Nature before officials can decide the fate of the tree, which is thought to be more than 600 years old.
Mr Wright said the attraction was running as normal and the tree would only be cut down as a last resort.
Living Landmark Award
He said: "We have reported the incident to English Nature and now have to wait for their response.
"We would only take such drastic action as cutting the tree down as a last resort, particularly with a tree as majestic as this."
The site is one of four attractions which have made it to the final of the Lottery's Living Landmark Award.
The forest will compete against a bid to extend the national cycle network, the Eden Project in Cornwall and the Black Country Urban Park in a televised public vote in December.
The £50m prize money would be used to create a new visitor complex and a 155-mile network of paths and cycle ways across the forest.
The county council has said that, regardless of the outcome of the lottery bid, the current visitor centre, which opened in 1976, will have to close by 2010 to protect the surrounding habitat.
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