"When he's 18 we'll talk again," Giovanni Bia told Sky Italia.

"I think Manchester will ask us to sign a five-year deal and I think that would be logical because it makes no sense to lose a lad at 21. We haven't talked about figures."

The 17-year-old, who came through the ranks of Lazio's youth team, showed a glimpse of his potential with two match-winning displays in the Premier League.

He scored the decisive goals in United's two successive wins over Aston Villa and Sunderland respectively.

"He has got something special about him, the boy," United manager Alex Ferguson told the club's official website.

"He's just got that instinct that goalscorers have. He has good movement and he's quick."