He told the Daily Mail: "I still do not understand the real motives of United and think the whole thing set a bad example for football. It is incredible that in the modern age - in the 21st century - there exists a situation where United will not sell to Liverpool.
"I only have good memories of the supporters and my team-mates but I would rather not give my opinion about the directors."
Although there was nothing in Heinze's contract that prohibited him from moving to Liverpool, when he appealed to the Premier League in August they ruled that United did not have to sell him to the Anfield club.
The 29-year-old Argentina left back insists that he is happy at Madrid but admits that he would love to knock United out of the Champions League. He added: "I really wanted to play for Liverpool but it is forgotten.
"During the summer I dreamed of playing in Anfield but the reality was different.
"I don't think often about revenge but it is certain that I want to play against Manchester United in the Champions League.
"That would be a big match and one without a clear favourite. But I would fancy Real.
"Manchester United never believed a big-name club would ever want me but I have proved them wrong and now I can't ask for anything more.
"This has just begun and there's a lot more to lay on the line."