The highly-rated 20-year-old is currently in London as he prepares to compete in the Olympics with Brazil.
Although the Blues have already secured midfielders Eden Hazard and Marko Marin, speculation has persisted recently that they are determined to add Oscar to their ranks.
For his part, Oscar reportedly told journalists in Rio before travelling to England "I'm staying" when asked about the possibility of a move to Stamford Bridge. And Di Matteo was equally coy when asked to clarify the 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 the club's official website.
"I know there has been speculation 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."