Ibrahimovic left United for LA Galaxy last week.
Raiola told Quote: “Zlatan's the cleverest of them all – and the richest.
“He has it within himself to be worth £1bn. He's incredibly intelligent and active in the market. I only have to tell him something once.
“Ibra is invested in gaming, tech start-ups and diamonds. He's already sold big shares to hedgefunds which no-one knows about. He's earning far more away from football then he does in it.
“When I do a deal for him, he jokes: 'You're going to steal a lot of money from me again, aren't you?'
“My answer to him is always the same. 'First, I make you rich – I can't steal from the poor, can I?'
“But it's the same when all my players are finished. They will have a lot more money than when they started.
“I try to protect them from financial blunders. For instance, I have an agreement with the banks that they let me know when the players spend big.
“I've told them that Amsterdam is the cheapest capital in the world. I've told them: 'Buy every property there that you can lay your hands on.' Winners have a plan, losers have an excuse.
"It's a good job for those big property tycoons that I went into football – otherwise I'd have owned half of Amsterdam."