Martyn Ziegler: Ronaldo is priceless and irreplaceable

One day, perhaps this coming season or perhaps the season after, it will dawn on Manchester United's owners that Cristiano Ronaldo was irreplaceable.

Although £80m in the bank softens the most painful blow, Ronaldo was as close to a priceless asset as any footballer can get.

This could well be the end of an era for United. They have lost key players before such as Roy Keane, David Beckham and Eric Cantona, and suffered a blip before they rebuilt under Sir Alex Ferguson but Ronaldo is the best player in the world, bar none.

We may have baulked at his diving in his early days, been put off by his petulance and preening and decried his air of arrogance but it is a simple fact that, whoever United splash out on to replace Ronaldo this summer, they will be a lesser side without him.

Who will come in? Franck Ribery? David Silva? Good players, sure, but not at Ronaldo's level, nowhere near.

Dribbling, shooting, passing, heading, free-kicks - and what free-kicks - he really has it all.

What about those who are almost at his level, such as Lionel Messi, or Xavi, Andres Iniesta, Kaka, Fernando Torres, Steven Gerrard, Michael Essien and Cesc Fabregas?

Barcelona will not sell their best players, even for £80m, for that would be tantamount to suicide, especially with the return of the galacticos era to Real Madrid.

As for the others: Kaka has just been signed by Real; Liverpool fans would storm the Anfield barricades if any move were made to sell Torres or Gerrard to United; Chelsea are so rich - still - that they do not have to sell anybody; and if Fabregas is going to go anywhere it would be back to Barcelona, not Manchester.

As Manchester City are finding out, you can have the biggest bank balance in the game but there is a limited supply of truly world-class players out there.

This was of course Ronaldo's decision too and though his previous overt flirting with Real Madrid had diminished of late, to many that was merely a sign that this time he really did want to go.

United fans will try to console themselves with the thought that Ferguson will be able to embark on the kind of spending spree Imelda Marcos enjoyed with shoes.

But of course it is not as simple as that. Not these days. The Glazer family run Manchester United as a business and blowing this £80million windfall is unlikely to be their chosen course of action.

Last year Red Football, the parent company of United and its various offshoots, returned a loss of £44.8million, increasing the Glazers' overall debt to an eye-watering £649.4m.

Ronaldo's sale will no doubt help United - the club rather than the parent company - record even higher profits for this year but with Red Football needing to service interest payments of £69m a year, no one should rely on the transfer fee being merely added to Ferguson's existing transfer kitty.

When one adds the Carlos Tevez factor into the United equation, the challenge becomes that much more daunting for Ferguson. If he wants to keep the Argentinian it will cost the club £30million.

If he does not, then he needs to find replacements for both him and Ronaldo.

What this world-record deal and Kaka's £56million move shows is that a big gap is beginning to develop. The small pool of rich clubs is shrinking - now perhaps it is just the top four Premier League clubs plus Manchester City and Barcelona and Real Madrid who can compete for the stars.

Increasingly, the world-class players are going to command staggering transfer fees, and staggering wages, and some analysts believe we may even see a slight drop for those at the next level.

Ronaldo's world-record move poses uncomfortable questions for United in terms of how far they can go to compete with their rivals at home and abroad.

The first answer will come from how much of the £80m Ferguson gets to spend.

The definitive answer will come in the next two seasons when we discover just how much United have suffered from Ronaldo's departure.