The 21-year-old midfielder, who joined the London side from Internacional at the beginning of last season, has started every game under the Portuguese so far this season, scoring the opening goal in the Blues' 2-0 win over Hull City Tigers.
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"It's been great to work with Jose Mourinho. He is one of the best coaches in the world," the Brazilian told reporters.
"We have seen he has already had a lot of success at Chelsea and I am just really happy to have the opportunity to work with him.
"You can already see the influence he has had on us during the first few games and I hope the team will be able to continue to grow under him, as I will also be able to grow as a player.
"As early as pre-season, we could see the belief with which he works."