The 19-year-old Kean joined Everton from Italian champions Juventus in August on a five-year deal for a fee of around 27.5 million euros ($30.49 million), but is yet to score in 13 Premier League matches.
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He struggled under former manager Marco Silva while Duncan Ferguson, Everton's interim boss before Ancelotti took charge, brought him on as a second-half substitute against Manchester United this month and took him off before the game finished.
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"When I was a player I remember Platini arriving at Juventus from Saint Etienne (at 27). It took him six months to adjust and that was Platini," Ancelotti told the British media.
"I had the same problem with Hirving Lozano when he came to Napoli and he was two or three years older than Kean... We should always be patient with young players.
"Kean is a player we tried to sign when I was at Napoli but he chose Everton. He has fantastic quality and I'm sure he'll be a top talent but he's 19 and everything is new for him here."
Italian Ancelotti will take charge of 15th-placed Everton for the first time against Burnley, who are 10th, on Thursday.
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