United have reportedly made the Aston Villa playmaker their top target for the upcoming summer.
And Warnock has urged the Red Devils to simply 'just pay the money' for the 24-year-old.
"I think he'd be a great acquisition for them, I think he's made to measure," the veteran manager told the Alan Brazil Sports Breakfast.
"When you think about Cantona, those players who have something magical, he fits that bill as a youngster.
"I think it would be a great signing. Man United are in a situation where they should just pay the money.
"I've got to say, in the past even when we [Cardiff] played a game against them [Villa] in the Championship, I've not worried too much about Jack. We've man marked him and thought he'd just give the ball away.
"But he's matured. I think over the last 18 months or two years he has matured beyond all recognition and he's going to get better .
"Because he's a bit of a flamboyant player, managers sometimes think twice about that in a team situation, but his contribution now…
"He's got everything. He just glides past people.
"When you look at the other lads in his position, the Maddisons of this world, Jack is the one who will score the goal out of nothing. He's the one against the top teams who will turn a game on its head just by giving him the ball.
"You can't mark him, he's unplayable at times."