Heinze joined Real Madrid in an £8million deal last week.
Ferguson said: “A lot of fans will be asking what all this was about but it started a long time ago.
“I was disappointed with Gaby from the time he joined us because he chose to play for Argentina in the Olympics in Athens in 2004 and didn’t come to us until the end of that September.
“His first season was fantastic but the day before he got his bad injury his agent came to our hotel and asked if we could sell Gaby. After one year I thought it was an absolutely distressing signal to put out.
“We allowed him to train in Spain and really he prepared to have himself fit to represent Argentina in the World Cup, which we couldn’t do anything about.
“We were not happy especially as he came back unfit from the World Cup.
“Meanwhile all through that time his agents kept having meetings with (chief executive) David Gill asking to leave or double his money.
“They wanted him to be the top-paid player, which is absolutely ridiculous given the quality of forward players we have.”