Luiz was dropped for Chelsea’s last three Premier League matches against Manchester United, West Bromwich Albion and Liverpool.
Conte said he was unlikely to start midfielder Victor Moses, who is fit again after more than a month out with a hamstring injury.
“I can tell you who are the players not available,” the Italian told a news conference on Tuesday. “Luiz for a knee problem… I must be honest at the moment it is difficult for me to answer (how long). It will be up to the doctor to assess it and take the best decision.”
Midfielders Charly Musonda and Kenedy will also not feature while forward Michy Batshuayi, who has not played since the end of October, is working his way back to fitness from a foot injury.
Conte is conscious of the need to rotate his squad over the busy winter months and said it was crucial for Chelsea to keep everybody fit if they are to have any hope of reeling in league leaders Manchester City.
City are eight points clear at the top and 11 ahead of third-placed Chelsea.
“The most important thing for us is to have all players available. I think November, December and also January it will be very busy,” Conte added.
“Don’t forget that if you play every game and you stop to train the probability to have an injury is very high.”
Conte refused to concede that the title was out of reach, and pointed to how his champions had improved after a less-than-ideal start to the campaign.
“We started the season with a lot of problems,” he said. “I think we have the points that we deserve and Manchester City is doing something extraordinary – to win every game, to draw only one game it means you are having a good path.
“But the most important thing for us is to look at ourselves and try to improve. We are becoming more solid. We are finding different solutions now in the tactical aspects. We have to continue to work and do our best.”