Villa face Derby in the Sky Bet Championship play-off final at Wembley on Monday.
Grealish would be expected to leave if Villa lose the £170million showdown despite signing a new five-year contract last September.
Tottenham were interested last year after Villa's play-off final defeat to Fulham but failed to agree a fee and Smith is not contemplating selling his star.
He said: "If we don't go up he'll cost someone a hell of a lot of money if they want to buy him. For me he is committed to Aston Villa and we've not even spoken about it otherwise.
"He's signed a brand new contract at the start of the season, committing himself to the football club.
"He loves Aston Villa and he'll want nothing more than to get promoted with Aston Villa."
Grealish has been Villa's inspiration in their late run to the play-offs, scoring four times in their club-record run of 10 straight wins.
He scored a stunning volley when Villa beat Derby 4-0 at the start of March, his first game for three months after returning from a shin injury, which kickstarted Villa's winning run.
But Smith is keen to lift the pressure off the homegrown 23-year-old.
"That's something right from the off we have played down. It is not about one person or pressure, it is about the team," he said.
"If players perform as a team you have more chance. It is not down to Jack Grealish.
"Yes, Jack's has got that little bit of brilliance but so has John McGinn and so has Tammy (Abraham) and (Anwar) El Ghazi, Tyrone Mings.
"We won't put any pressure on any individual and talking to Jack he doesn't feel that either, he has relished being the captain of Aston Villa and is looking forward to the game and hopefully getting that win."
Villa's parachute payments end this season after their Premier League relegation in 2016 and they were struggling financially under former owner Tony Xia.
Wes Edens and Nassef Sawiris bought the club in July and Smith is confident plans are in place whatever the result.
"You have to prepare for winning or losing," said Smith.
"One way or another, on Monday night we will either be a Premier League team or a Championship team and you have to have two scenarios for it.
"But the difference this year is that the owners we've got are fully behind the club and it's on an even keel and hopefully moving in an upwards direction."
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies