The Brazil international believes his compatriot has matured since arriving from Internacional, but he is still trying to help the midfielder with his quiet personality
The midfielder's Stamford Bridge career started in outstanding fashion as he bagged two goals against Juventus in the Champions League, but since the arrival of Rafa Benitez he has often found himself on the bench.
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Fellow Brazilian Luiz believes that his problem at the moment is his shyness, but he is certain that will fade away just like his insistence on shooting whenever possible.
Luiz told reporters: "I try to help him every day with this [his shyness]. I tell him he's an amazing player with the talent to make the difference and change every game. I tell him to be happy and trust in his football.
"Some players need this. My job is to give confidence to the guys like Oscar.
"He is so shy but I say, 'come on, you have the quality to be in a side with the best players in the world and you have the opportunity to show that.'
"Some guys in Brazil don't, they have the quality but they don't have the opportunity to come to Europe and show the world what an amazing player they are. So, I say, 'come on, don't be shy, show your quality'.
"He is a young guy who wants to learn every day. Every game now he is more intelligent. He can grab the game and he's waiting for the moment to decide the games.
"When he first came he was so excited and wanted to do everything. With the first ball, he wanted to shoot. But now he's more mature. We need this guy for a long time at Chelsea."
With Chelsea's strength at centre-back, Luiz has also found himself on the bench at times. Though he admits it is frustrating, he says he understands the need for squad depth.
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He continued: "When you are on the bench and you are fit, it is a bad feeling.
"I don't like it but I understand sometimes you need to play other players. If you want to do just your own thing and play always, play an individual sport like tennis."
Chelsea face a tricky test away to Steaua Bucharest on Thursday night in the Europa League, and although the club's focus remains finishing as high as possible in the Premier League, Luiz would love to add another European title to his CV.
Luiz said: "This is a great opportunity to win a European title. Last season was Champions League and people were happy but we are hungry again.
"This is the way to think if you play for a big club. We are looking for the Europa League title."