Having sold David Beckham to Real Madrid, Sir Alex Ferguson had identified the Paris Saint-Germain playmaker as the ideal marquee signing to replace the departing England captain.
However, with the deal almost agreed, Sandro Rosell, who at the time was in the running for the Barcelona presidency, was able to convince the 34-year-old to pick the Camp Nou over Old Trafford.
"It almost happened with United. It was a matter of 48 hours, but Sandro Rosell had told me way before I got the offer: 'If I become Barça president, will you come?' I said yes," Ronaldinho told FourFourTwo.
"It was only a matter of details with United when Rosell called to say he was going to win the elections there. I had promised to him that I'd play for Barça. It was a quick negotiation. I told the English I had chosen Barca."
Ronaldinho, now of Atletico Mineiro, went on to spend five years with Barcelona, where he won two La Liga titles and the Champions League once.