Rojo joined United in a £16 million deal before the transfer window closed in August, which saw Portuguese winger Nani move in the opposite direction on a season-long loan.
However, the transfer was in danger of collapsing amid third-party ownership problems between Sporting and Doyen Sports, who owned 75 per cent of the player's rights.
"It was a huge surprise when I was told United wanted to buy me," said the 24-year-old, who is sidelined with a dislocated shoulder.
"I was in Portugal when my representative told me. He asked me to stay calm but I could not. I started living this dream.
"I could not think of anything else. I would call him every day, but when it seemed the transfer would not happen then I refused to work with Sporting.
"That was when Veron played his part in the process. He was like a strict father to me, scolding me.
"Veron called me one day when I had refused to train with Sporting and said 'Do not be stubborn. If Manchester United wants a player then they will not let you escape.'
"And so I went back... and the transfer went ahead."
