The Italian refused to be drawn on continuing reports that a €32 million fee has been agreed between the Blues and the Porto Alegre club
The Premier League club are understood to have had a €25 million (£19.6m) offer already rejected by the Brazilian club, prompting president Giovanni Luigi to admit that the youngster could be sold if a further bid was suitable.
And, despite reports in Brazil suggesting that the 20-year-old was temporarily released from his Olympic duties in order to complete a medical with the Blues ahead of a €32m (£25m) move, Di Matteo was reluctant to reveal too much on the current situation.
"I can tell you that he's not a Chelsea player so it's difficult for me to talk about a player that doesn't belong to us," the Italian told reporters.
"I know there has been speculation that we are interested in this player and in due course, if there is anything to announce, we will do. All I would say is that he is a very young, talented midfield player."
Di Matteo, who was speaking in America ahead of the club's pre-season friendly against the Seattle Sounders, revealed that winger Florent Malouda had joined up with the squad despite much speculation linking the winger with an imminent departure.
Santos were thought to be close to sealing the France international's signature, but wage demands look to be halting progress.
Di Matteo added: "Players are now slowly returning, Malouda was back today and we expect the others to come when we are on the east coast.
"I still haven't had a chance to speak to Florent, so I need to speak to him first and see what his intentions are, then we will see what the best interests are for him and the club.
"At the moment I am very happy with the squad. We have a good squad, a very good team and have new players with us already. Our job is to try to integrate them into a team that was very successful last season."