Luiz has been linked with a series of clubs during the summer, including speculation of bids from Barcelona and Manchester City.
Di Matteo said: "Luiz is definitely part of our long-term future here.
"It's normal he gets interest because he is a Brazilian international centre-back but we have three internationals for that position and it's great. We need to have that for a club like us."
Luiz is expected to replace the injured John Terry in Chelsea's team for their Premier League match against Newcastle United after the Blues captain suffered a neck injury.