Despite being Chelsea’s player of the year in the two seasons before Mourinho’s 2013 return to Stamford Bridge, Mata failed to establish a regular place in his new manager’s side.
A substitution in a New Year’s Day win at Southampton spelled the end for the Spaniard, who was sold to United for £37million later that month.
When the pair were reunited last summer, many speculated that Mata may once again be forced to move clubs, but the 29-year-old claims his “normal” relationship with Mourinho was always unlikely to be a problem.
“The context, the club, the template and the way of playing changes from one team to another,” he told El Pais, the Spanish daily newspaper.
“I’ve never had a bad relationship with him. We’ve never had an argument. Our relationship is normal.
“Simply, in Chelsea he wanted to play in a certain way and at United, there are other types of players more in line with my characteristics. We are both the same, we have not changed.”
Mata has been one of United’s more consistent performers in a middling first season under Mourinho’s management.
The former Valencia and Chelsea attacking midfielder had made 37 appearances over the course of the current campaign until he sustained a groin injury in March.
Mata was thought to be out for the rest of the season, but made a surprise return to United's matchday squad as an unused substitute in Sunday's 1-1 draw with Swansea City.
United face Celta Vigo away from home in the first leg of their Europa League semi-final tie on Thursday night.