The 20-year-old Brazilian signed a five-year contract with the west Londoners in July in a deal reported to be worth around £25m following weeks of speculation linking him with a switch to the Blues.
Di Matteo, whose side take on Manchester City in the Community Shield at Villa Park on Sunday, revealed he kept a close eye on the attacking midfielder before and during his participation in the London 2012 Olympics with Brazil.
And the Chelsea boss is hoping he will develop into a Stamford Bridge star in seasons to come.
“I watched him [Oscar] in the Olympics, before the Olympics, and he will certainly add a lot of quality to our team,” Di Matteo told a news conference on Friday.
“He is still a young man and will be able to learn a lot from the players we have here, and the mentality of the players here.
“There are plenty of trophies to win this season and we have a very driven team and players who are never satisfied with what they have done in the past.”
Di Matteo also moved to play down speculation linking striker Daniel Sturridge with a transfer away from Chelsea, although the Italian did admit that the Team GB forward is sure to face competition from Fernando Torres for a spot in the first team.
“He is part of the squad, of the team, and still has a lot to give,” said Di Matteo of Sturridge, who was named in Roy Hodgson’s England squad for the friendly against Italy on Wednesday.
“He still has a lot to learn as well but we are hopeful he can develop even more and become a great player for us.
“He did very well to recover from his illness in a short period of time. He is a very exciting player and it’s great for him to be involved in the England squad.
“He has the ability to play in more than one position. He made it quite public he likes to play as a number nine but there is competition, which is good, and we will see as the season starts who is going to play.”
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