The Spanish giants were strongly linked with Luiz in the summer and are believed to be planning to revive their attempts to sign him when the transfer window reopens.
However, Mourinho has played down the speculation, insisting that the former Benfica star, who has made only five Premier League appearances for the Blues this season, is needed for first-team duties. He also suggested that there is unlikely to be much activity, in or out, at Stamford Bridge in the New Year.
"Everything is clear. He's our player and we are happy he's back in a moment when we need him and John in defence," Mourinho told reporters.
"The market is open in January but I don't think we will be buying or selling. There has been no contact from other clubs or from his people."
Luiz, who made his comeback from a six-week layoff with a knee injury in midweek, is expected to start against Crystal Palace on Saturday, with Gary Cahill suffering from a quadriceps problem.