The Spanish midfielder was offloaded by the Portuguese from Chelsea to United in January 2014 with plenty of reports ever since suggesting he was forced out.
However, Mourinho has attempted to clear up the confusion by indicating that Mata instead wanted out at Stamford Bridge which prompted the Blues to do a deal with the Red Devils.
"First of all, I think maybe all of you misunderstood what happened in our previous club because I never told Mata to leave," he said in an interview with Sky Sports.
"I never pressed the club to sell him.
"It was his decision and only his decision, and I don't like players that want to leave.
"That's why I think every player has a price because if one day a player wants to leave it is because he does not want to be with us.
"If the player doesn't want to be with us, goodbye - be happy where you want to go. Juan at our previous club was not so happy because he was not my first choice at that time. He wanted to play every game.
"He had a fantastic offer from a big club like Man United, he wanted to leave. My previous club had a great offer, we thought that was financially very much acceptable.
"We were not with this old-fashioned idea of, 'I don't sell players to my direct competitors inside of my own country'.
"We sold him to Man Utd and done. Nothing else."