The Brazil international striker has revived his career this year after a spell on-loan at Sao Paulo and now working under Mourinho at Inter.
Cunha said: "He is young and needs time to catch up. He had no father figure, needs the affection of a child and this is what Mourinho has understood. The Portuguese coach understood how to handle him and the results are there.
"He is good. I often had to take a hard line with him. He must understand that many of those around him are doing so because we want to see him back to his best."