The defender has been linked with bigger clubs this year.
Gold, speaking to SportsDirect News, said: "We are not selling James Tomkins - he's on a long contract and is still only a young man.
"He's an absolutely top prospect and were he to be available it would not be easy to buy him as we have a very high valuation on him.
"This is no longer a selling club. We are moving forward into a big future and we will therefore be keeping our biggest players - James is one of them."