The Brazil international was replaced by 21-year-old Andreas Christensen for the United game and local media reported that he had been dropped after falling out with Conte, but the Italian said on Friday that omitting a player was "normal".
"Yes, David Luiz is in the squad," the Italian coach told a news conference. "It was a technical decision and every player has to react well... to accept my decision. It is normal."
Asked about his relationship with Luiz, Conte said: "I'm here to talk about the team before an important game against West Brom and not about a single player."
Champions Chelsea are fourth, a point behind United and Tottenham Hotspur, but trail leaders Manchester City by nine points ahead of the visit to struggling West Brom.
Conte praised Christensen for handling the pressure of such a high-profile game and said the Danish international, who spent the last two years on loan at Borussia Moenchengladbach, was proof that Chelsea's policy of loaning out youngsters worked.
Chelsea have been criticised for not giving youth a chance, and in Ruben Loftus-Cheek and Tammy Abraham have two players who have impressed so much on loan at Crystal Palace and Swansea City respectively that last week they made their England debuts.
"I read Ruben's interview, and he said that his path is perfect and to play regularly this season is very important for his development," Conte added. "Then to come back and play for Chelsea with greater maturity.
"It's the same path for Christensen. He played for two years on loan and now he's playing regularly for Chelsea. He's young but an important Chelsea player."
Michy Batshuayi, Chelsea's back-up for striker Alvaro Morata, will miss the West Brom game with a foot injury while midfielder Danny Drinkwater, who took a knock to his calf against United, returned to training this week.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Ken Ferris)
