The center back, 25, missed the Blues' 4-2 win over Reading on Wednesday with an injury but was in Catalunya the next day, sparking rumors of a switch to La Liga - though his Spain trip was to fulfil a commercial obligation for a sponsor.
And Di Matteo was quick to stress the importance of the Brazilian to the future of Chelsea, shrugging off any suggestion that it needs to sell players this summer.
"I don't feel any pressure in that sense," said the Italian coach to the Daily Telegraph. "This club has been very, very successful in the past and I don't see why any player should want to leave us to go anywhere else.
"We always compete for trophies; [Chelsea] are a very ambitious club with an ambitious owner, a great group of players that over the years have won a lot but still have the hunger to win more.
"Competition is hot, we have great facilities, everything.
"David Luiz is part of our long-term future here. It's normal that he gets interest. It doesn't concern me. I think the player will be here in the long term."
The west London club has been very active in the transfer market this summer, bringing in (among others) Eden Hazard, Oscar and Victor Moses.
Di Matteo said: "If you look at the profile of the players that come in you are looking at players who will be here for the next four or five years.
"They are all very young players. You are looking for them to be the platform for the future of this club.
"I don't expect a revolution or anything like that. It's a slow process to try to get the players slowly into the team and try to build a team for the future.
"You are looking at investment in the next cycle of four or five years."