The Blues boss has ruled out a move away from Stamford Bridge for the Brazilian defender amid speculation that the Liga champion is readying a big-money offer.
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 the club's latest preseason match.
"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 preseason preparations with the squad after overcoming an injury.
"Frank has got to start playing now," Mourinho said.