The French youngster's switch angered Ferguson, who has since complained about the manner of the midfielder's transfer.
Former Chelsea striker Casiraghi revealed the first push to get Pogba out of United came from a French agent. He told TMW: "It was run by a French guy (Oualid Tanazefti), who was good and had the courage not to let him renew the contract, despite pressure from Ferguson.
"This guy then suddenly realized he could not keep Ferguson away and so called Mino Raiola for the operation. Facing Raiola, Ferguson began to backpedal.
Casiraghi insists Pogba is "a great guy".
"Paul is a great guy. Indeed, I do not understand why he arrived late to training last time. Everything that Paul has won he earned by working hard."