#4 David De Gea
Manchester United paid £18M to lure David De Gea from Atletico Madrid in 2011 and it looks like he is the only reason why this list will need an update sometime soon after rumours have been circling around about a £60M deal in transit from Spanish giants Real Madrid.
De Gea is already considered as one of the best goalkeepers in the world at the moment and United will not be looking to let him go on the cheap or not letting him go at all.
After a shaky start to his career at United where he was criticised by fans and pundits alike for poor decision making and not being commanding enough inside the penalty area, De Gea quickly earned the plaudits when he eventually found his stride.
Ever since then, the Spaniard has never looked back and has proved to be an invaluable asset to his club.