This week they are finding out they are anything but.
Any way you want to look at it, they are in Real Madrid's shadow. In terms of prestige, global power, European Cups, league titles...you name it.
Cristiano Ronaldo knows it. Which is why he's kicking at the emergency exit door at Old Trafford.
United had a good season, but they got lucky in Europe and only won the Premier League because Chelsea shot themselves in the foot so many times last season.
Ronaldo can make himself a better footballer, and a wealthier individual, by leaving United for a bigger club.
Just as Michael Carrick improved his lot by leaving London for Fergie. As did Rio Ferdinand by moving from Leeds.
Big clubs feed on the better players of smaller clubs. That's what Real Madrid are now doing with Manchester United.
Fergie can have the biggest strop of all time, he can scream himself redder than he's ever coloured his cheeks before, but it won't make any difference.
The choice in front of Ronaldo is another season bullying flat-footed English defenders alongside the likes of Wes Brown, Darren Fletcher and Ji-sung Park in the Manchester rain or showing off his skills in the sunshine of Madrid in a team of superstars.
Bit of a no-brainer, really.
United, you're not quite as big as you think.
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