The Blues boss has ruled out a move away from Stamford Bridge for the Brazilian defender amid speculation that the Liga champions are readying a big-money offer
Goal revealed last month how the Liga champions have stepped up their search for a centre-back by making a €29 million move for the Brazilian, while Gerard Pique has admitted it is difficult for Barca to sign a defender.
But the Blues boss praised the 26-year-old Luiz's ability and insisted he will be used in the team after he sat out Chelsea's 2-0 over Milan in their latest pre-season friendly.
"David has come back with us fantastically and we have to use his quality," Mourinho told reporters.
"He has big self-confidence and self-esteem, especially when he comes up from the back with the ball.
"Can he improve defensively? Of course. But it is my job to try always to improve players."
The Portuguese coach also confirmed that midfielder Frank Lampard is ready to begin his pre-season preparations with the squad after overcoming an achilles injury.
Mourinho confirmed: "Frank has got to start playing now."