United, European finalists nine years ago in the era of Jim McLean, estimate that relegation from the Premier League last May cost them around pounds 1m in lost revenue.
Thistle, who have survived in the top flight by the skin of their teeth over the past four seasons, could face a hazardous future if they lose their status.
The sides are locked together after Sunday's play-off first-leg at Firhill which ended 1-1. Now it is a winner-takes-all contest over 90 minutes, extra time and penalties if need be.
Yesterday the managers, Murdo MacLeod of Partick and Billy Kirkwood of United adopted different approaches to matches which could affect players' future livelihoods at both clubs.
Kirkwood has no hesitation in agreeing that the match, in front of a 12,600 sell-out Tannadice crowd and with live coverage on Grampian Television, is the most important in United's history.
And he wants no repeat of the 1-0 defeat by Dunfermline in United's most recent home game which cost them the First Division championship and automatic promotion.
"We blew it the last time because the crowd and the players were on edge after losing an early goal," he said. "The fans were all desperate for something to happen and that desperation was felt by the players. I would ask the fans to be patient because we can't win this game in the first 10 minutes or even in the first half-hour.
"However, I have to be happy that we don't have to claw back a deficit in this game and I felt we deserved our draw at Firhill. At the same time no one at this club is getting carried away because we know we haven't done anything yet. It is a one-off game of 90 minutes on a decent pitch at which a winner must be found so we will giving it everything we've got."
United are without the suspended Maurice Malpas but Mark Perry, who missed the game at Firhill, is likely to be fit. Striker Gary McSwegan could start the game after coming on as a substitute on Sunday.
The Tannadice players are said to be on a pounds 10,000-a-man bonus to win, but MacLeod rejects the notion that cash will inspire either side. "Money can't win you the game," the Thistle manager said. "It is a bonus and that is all it is. When you go out to play in a match all you should be thinking about is winning.
"There is no fear of losing here. I've heard no negative thoughts around Firhill and we are treating it like a cup final. My young players like Jim Slavin, Billy McDonald and James McCue haven't been in the game long enough to worry about it - this is all new to them."Reuse content