Speculation has linked Mata with a summer exit from Stamford Bridge but Mourinho has stressed that the Spaniard has a key role as the only left-footed player he feels is comfortable on the right.
"Of course he fits into my plans," Mourinho said. "I have my idea about him, about where he produces better and where he has more difficulty.
"We will try to help him perform better in those situations. I've always liked a right-sided player to be left-footed.
"I started with (Arjen) Robben and (Damien) Duff, then (Goran) Pandev at Inter, and (Angel) Di Maria and (Mesut) Ozil. Many clubs do it. It's more than a tendency.
"I like wingers coming in on the inside for the penetrative movement, for the pass, for the shot. And Juan is the only player we have to do that on the right.
"On the left we have (Eden) Hazard, Victor Moses, Kevin De Bruyne, Andre Schurrle. Juan is also very comfortable playing as a No10. In between these two positions, he has a lot to give to the team."
Mourinho has often appeared more comfortable praising workmanlike players rather than star named such as Chelsea's player of the year and the Portuguese boss believes there is logic to this.
"I am not the kind of guy who makes life easy for the great players," he added. "This kind of player is the last I praise.
"You have to praise the guys who play to their limits, who give everything. They are not superstars. They are just good players trying to support their teams.
"Don't get me wrong, I still prefer the top players, the guys who win you matches and make the difference. But if they are great, they have to give more than the others.
"For me, to praise an ordinary player is easy. For me to praise a top player is not. When a player is different and has more potential than others, he has to use his talent in a good way."