I'm always in favor of sending players out on loan, because I think it serves two major benefits:
First - the obvious one; a chance for a young payer to experience first team football.
Second - it allows the player a taste of life outside of Manchester United. Not every club around the world is as glamorous as United. Not every club has plush, top quality training facilities, or the heightened media attention, or the worldwide supporter appeal, or the "family feel" like Manchester United. So sending a player out on loan hopefully lights a fire under their belly to come back and prove that they want to be here and experience the "good life" for lack of a better term.
We are seeing now with Welbeck, just what going on loan can do to someone. If anyone read Beckham's biography, then you know how important he regards his brief loan spell out to Preston North End in the context of his entire career - even if he only played 5 matches out there.
So I'm always in favor of sending players out on loan because in truth, unless your in a situation like Rodrigo Possebon found himself in around this time last year (which is extremely rare), loan moves for young players don't really hurt. The only thing I would question in regards to Fabio going out on loan, is whether or not Ferguson a) sees him in his immediate squad plans, and b) whether Fabio has it within his personality to benefit from a loan move. Let's face it - his brother Rafael is here, and we know that Anderson and Nani (the other Portuguese speaking players in the squad) are all quite close to him and one another. Therefore, would it really benefit him taking him away from that positive comfortable environment? Finally, considering his age - he's just 20 - is he the type that will go out and tackle the world, or the type that Ferguson needs to keep cocooned and sheltered? Sir Alex knows best.
In short - I'm in favor of any loan move, especially for players that are so promising (Cleverley, Welbeck, Fabio) but just can't fit into the side at the moment. The question is, does Ferguson think a loan move will benefit Fabio.