I see a better chance of him playing to his potential at City, because they might actually let him play, where Barca would bench him/force him to adjust to their system (that I don't think suits him).
why would be illegal? It's just a co-own deal for a player, he plays for one team and then it' all resolved, one way or another. It doesn't seem to be a popular way of doing business outside of Serie A but is really popular in Italy.
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As for Sanchez, I think the best team for him would be ManU, then Barca and probably the worst City - Mancio just isn't much of a coach and I think Sanchez would struggle with his adjustment to a team full of big egos and the EPL altogether, should he go to City.
Udinese could build a new team with 50 mill and still have cash left over.
I have to agree with Jack, he'd thrive at United. A 4-3-3 with him and Rooney on opposite sides of Chicharito would be nasty. I don't see him at Barca though.
2 season if he does not win anything. If he wins first season then does not win anything second season he's gone. If he does not win Champions League in two years he's gone also.