Mata is on the verge of completing a £37m move from the Blues to Old Trafford, and after a season of frustration at Stamford Bridge, Mourinho has admitted that the 25-year-old deserved a chance to play more games.
The 50-year-old told reporters: "I think that this club is a special club and it cares for people. It is very respectful of its players and especially those who wrote history and Juan is one of these.
"This is a fantastic opportunity for him. Another big club wants him in the country that he want to stay in. They have made the right offer for him, so, although lots of clubs feel that you should not sell to rivals, we are different.
"The player deserves respect and to play and because the offer is right, we allow him to negotiate, but we don't close the door."
Mata is expected to undergo a medical in Manchester on Friday.