The 21-year-old joined from Internacional for £6.5million in March, but stayed in Brazil to help his club win the Copa Libertadores, the South American equivalent of the Champions League, last month.
He will make his debut in the Carling Cup on Tuesday night.
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“He's like Socrates,” said Redknapp, searching for comparisons. “He looks like him, he runs like him. If he can play like him, we'll be alright. He's not a Robinho. He's a big lad, he gets around the pitch, he can tackle, he can pass it and play.
"We spoke to people in Brazil, we spoke to [former Brazil manager] Dunga and they all said: 'You've got a real good one there'.”
The Spurs boss could not make the trip to Brazil to watch Sandro in action but sent his chief scout Ian Broomfield to monitor the Brazil player for a month.
“We'll see whether Ian's got a job on Wednesday,” joked Redknapp. “He raved about him. I couldn't get out to Brazil to see him because it was in the season.”
He admitted that the 21-year-old is only the second player in his long managerial career whom he has signed without personally having watched him play live.
The only previous such purchase was Dutchman Marco Boogers, who joined Redknapp's West Ham United for £1 million in 1995, got sent off in his second game and faded into oblivion.
"Don't compare him to Boogers, give the lad a chance," said Redknapp, “You don't get into the Brazilian national squad if you're a mug, do you? Wherever you go there are good Brazilians.”
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