Manchester United made an offer to Bobby Duncan before he left Liverpool for Fiorentina on Monday.
Vincenzo Morabito worked closely with Duncan and his agent Saif Rubie in securing the teenager's switch to Italy earlier this week.
He told the Daily Mail, "It all started in April. Saif contacted me and we set to work to find new accommodation for Bobby.
"The boy did not want to betray Liverpool and said no to United who insisted so much with him.
"He could have gone to Lazio but relations with Liverpool are very bad and nothing was done.
"(Lazio manager) Simone Inzaghi would have made him grow a lot and I hope he is like that with (Fiorentina boss) Vincenzo Montella."