The centre-back, 25, missed the Blues' 4-2 win over Reading on Wednesday with an injury but was in Catalunya the next day, sparking rumours 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 they need 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 have 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."
Chelsea currently sit top of the Premier League heading into this weekend's round of fixtures having played a game more than their rivals, but Di Matteo played down hopes of beating Manchester United and Manchester City to the title this season.
"We need to make up 25 points [from where we finished last season in relation to the Manchester pair] and I don't think any team has done that in the history of the Premier League," the former West Bromwich Albion boss pointed out.
"City haven't lost any key players. United had the same points and they have signed Robin van Persie. They are still the two teams you need to beat."