The Royal Showground could be advertised for sale if plans to build an agricultural centre of excellence are turned down.
The Royal Agricultural Society of England (RASE) want to build the centre at the Royal Show's Warwickshire home but cannot due to a planning condition.
If trustees do not agree to the condition's removal, then the site will be marketed, a RASE spokesman said.
He added there was no obligation to sell it, even if marketed.
Hugh Oliver-Bellasis, vice chairman of RASE, said a letter had been sent to staff and to tenants explaining the society was seeking to get new planning permission to enable them to develop the centre of excellence.
"The difficulty is that we need to modernise an agreement relating to a planning consent," he said.
"We have made the Stoneleigh trustees an offer and we need to know whether they will negotiate or not."
The trustees have until 17 July to respond.
"If the deadline passes we shall market it, but that puts us under no obligation to sell it," the spokesman added.