The midfielder has been linked with Crystal Palace and Tottenham.
Grealish,23, may have to be sold to comply with EFL profit and sustainability rules if they miss out.
Smith said, "It would be crazy if we didn't get bids for him. But he has a long-term contract and he's a Villa fan.
"He is captain of the club now as well. There are an awful lot of things to keep him at this club."