The Dutchman was sacked as Red Devils boss the day after guiding the club to an FA Cup triumph over Crystal Palace in the 2016 final at Wembley.
Van Gaal is unhappy with how he was treated by the club, who he believes courted Jose Mourinho for the manager's job after he was sacked from his second spell as Chelsea boss.
"United put my head in a noose and I was publicly placed on the gallows. The pressure was enormous with my head in the noose and they went right behind my back," he told The Mirror.
"I think it was all orchestrated like a film and it was done very much behind my back right from January. My wife, Truus, told me that the attitude of the board had changed. Women have this intuition. They smell it.
"I never wanted more than two years anyway. Man United wanted three years. Suddenly, Mourinho was out after one-and-a-half years of my contract and I knew United wanted him one day. They told me only after it was leaked out and it was the biggest disappointment of my life.
"United did not discuss this with me. If they had come to me with the Mourinho plan then I could have said 'okay, let's give it everything for the last six months, complete commitment to each other and the team and then Jose Mourinho can take over.' They could have saved the last year of my salary by doing that but after what happened I made them pay every penny."
United paid out £8.4m to Van Gaal and his coaches after they were sacked.