Oscar joined Chelsea from Internacional in July but could only train with the rest of the Blues squad for the first time on Friday morning because of his commitment with Brazil at the London Olympics.
"He is a goal-scoring midfielder, a creative midfielder as well," Di Matteo told Chelsea's official website.
"In his career so far he has played on the left side, he has played there with the national team, and he has played behind the strikers and the number 8 role as well in a three-man midfield - so he is quite versatile.
"He had a very good Olympic tournament and he is a young man as well, let's not forget that, and I think he will be a very good addition for us. He has broken through to the senior Brazil team at a young age and you need personality to achieve that."