However, where does he rank amongst the most expensive players under 20 ever? The Daily Telegraph has revealed all, with the Red Devils featuring no less than four times in the top ten. Real Madrid, Chelsea, and Barcelona have also spent big on young players in the past, with various levels of success.
Signing such a player at such a young age obviously brings with it many risks, including but not being limited to potential injury problems and not living up to their potential. Although, United do have a relatively good record for buying in the age group.
Here are the ten priciest teenagers ever, and how they have each performed after their deals. Will Martial be a Pato or a Rooney?
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10) Alexandre Pato, Internacional to AC Milan, £15m
Still only 25-years-old, the Brazilian hasn’t lived up to expectations yet and is back in his home country with Sao Paulo FC. However, there is still time to return to Europe and prove his doubters wrong.