Sir Alex Ferguson admits he can only wonder what might have been had the former world footballer of the year joined Manchester United as anticipated.

When he set off for the pre-season USA tour in 2003, Ferguson believed the deal had been done.

By the time he landed in Portland, the transfer had unravelled and Ronaldinho had opted to join Barcelona.

The exact reasons for the sudden failure to conclude the deal have never been fully explained, although it is thought Ferguson holds former United, and current Chelsea chief executive Peter Kenyon responsible.

Having helped Barcelona to successive La Liga titles and a Champions League triumph last term, his potential impact had he joined United - who have won just an FA Cup and a League Cup during the same period - is incalculable.

Instead, Ferguson is left with the one silver lining to a big, dark cloud - namely the arrival of Cristiano Ronaldo from Sporting Lisbon in the same summer as Ronaldinho headed to the Nou Camp.

"I do think what might have been when I look at Ronaldinho," said the Scot.

"We thought the agreement with him was done until some events changed the course of history.

"But the good thing about Manchester United is that the club does not stop just because one player says 'no', or we fail to get him.

"We thought we had Paul Gascoigne but he changed his mind and went to Tottenham, so we signed Paul Ince and he was fantastic for us.

"Likewise, we tried to get David Hurst and Alan Shearer and ended up with Eric Cantona. What can I say about that?

"Something always turns up. Football is amazing like that. We did not get Ronaldinho but out of that came Cristiano Ronaldo."

Having lost David Beckham to injury, the organisers of Tuesday's celebration game to mark the 50th anniversary of United's entry into Europe and the Treaty of Rome will hope Ronaldinho makes it.

The star attraction of Marcello Lippi's European Select XI has been troubled by a thigh injury.

Liverpool duo Steven Gerrard and Jamie Carragher are scheduled to take part, along with departing Red Devil Henrik Larsson and Barcelona duo Lilian Thuram and Carles Puyol.