Along with United, Inter Milan have been linked with the Brazilian player. Both teams would have to dig deep into their pockets, with £50 million being the current asking price for the player.
Chelsea are also interested in him.
However, United are favourites at the moment. It has emerged that Madrid boss Jose Mourinho would be happy to talk to his old rival Sir Alex.
Jose would rather send Kaka to United than to his previous clubs Inter or Chelsea.
Sir Alex has stated that he will not be buying any players in the transfer window but has not ruled out any loan deals.
Ferguson is trying to find a club that will take Macheda on a loan, and Kaka would slot in perfectly in the gap he leaves. The striker force of Berbatov, Rooney and Kaka would leave teams quaking in their boots.
Kaka moved to Real for a massive £56 million deal in 2009, but now Mourinho says he is not suitable for the style of play in which the team engages.
It looks certain that Kaka will be leaving Madrid, even if it's as late as the summer. The intriguing question is whether he will choose United.