"Stewart is a smashing lad and we're delighted that he's at our club," the Boro chairman told The Times.
"Not only is he a fine player, he's a fine man as well and he's the kind of person we want here.
"He's midway through a five-year contract and we voluntarily entered contract negotiations with his agent at the start of this season. We made a substantial offer, which reflects Stewart's status at our club and in our team.
"Unfortunately, we have to deal with Ian Elliott, a man who, in any other walk of life, you couldn't imagine giving ten minutes of your time to. He has issued a statement which, when you study it, is an absolute contradiction. On one hand, it says Stewart wants to leave and then, on the other, it says that Stewart will play out the remaining two-and-a-half years of his contract. Well, what's it to be?
"Stewart will have seven or eight years left at this level and the fact that he appears to have put his career in the hands of Ian Elliott is a source of concern for me because I don't think that's in Stewart's best interests. We will be as supportive as we can to Stewart. We owe him a responsibility to look after him and we hope he'll sign the contract that he's been offered.
"He's never seen out a contract here because he's always been offered improved terms at the correct times as he's progressed. We would continue to do that. But his agent has a fanciful target which will not be realised at this football club or any other and, at this point in time, we have received no offers for Stewart. Our position is firm. We want him to stay, but the contract offer will not be improved.
"What would happen now if, heaven forbid, Stewart suffered a career-threatening injury over the next couple of years? His agent is playing a very dangerous game."