10. Radamel Falcao
Bought for: £3.9m by Porto on 15.07.2009
Sold for: £34.7m to Atletico Madrid on 18.08.2011
Colombian striker Radamel Falcao proved a worthy gamble by Porto to say the least. Not only did the lethal marksman score 40 league goals in two seasons, which included an unbeaten campaign featuring Europa League success, but his eventual sale to Atletico Madrid two years later yielded a massive return.
Falcao has since gone on to cost moneybags Monaco just shy of £50m and could well challenge for the player to acquire the highest accumulated transfer fee in football history.