1. Lionel Messi
An unsurprising candidate for such a list, I'm sure you will agree.
Given the outstanding individual and indeed team success he has enjoyed with Barcelona, it seems incredibly unlikely that Messi will ever seek to depart the Camp Nou or that the club themselves will look to move him on.
However, in the event that the 26-year-old does ever leave the Catalan giants, you can be sure - if he remains in his prime - that he will command a fee well, well in excess of £100 million.