The 21-year-old joined the Blues in July from Internacional and has settled in quickly to life at Stamford Bridge with the Champions League holders.
The Brazilian has netted several eye-catching goals already, most recently against Shakhtar Donetsk in midweek when he scored from fully 40 yards as Chelsea won 3-2 in the Champions League.
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"He's amazing, he will become a top player. Recently he has changed his style and has improved his build-up play," he told the Corriere dello Sport.
Dunga also spoke about two more of his countrymen Lucio and Felipe Melo, with the centre-back having to wait for a starting birth at Juventus, after suffering an injury early in the season.
"Am I surprised to see Lucio so little time on the field? I think it's only a matter of time before he plays, he pays for being injured early in the season," said Dunga.
"Could he leave Juve in January? He is one who always wants to play and I'm sure he is doing everything to convince Conte of his talents. I would be surprised if he left: Lucio likes difficult things and he's not a guy who leaves during battles.
"What do I say to him? To stay calm and use all the opportunities he gets. As soon as he becomes a regular he won't leave the first-team."
And, when also asked about Melo, who is spending a second consecutive season on loan at Galatasaray from Juventus, the 49-year-old said: "My 'old friend' Felipe Melo? He arrived at Juve at the wrong time. If he played with Pirlo he would be perfect."