#1 Lionel Messi

Lionel Messi and transfer news have never gone hand-in-hand. The Argentine has been with Barcelona for close to two decades now, making any transfer talk sound ridiculous. However, if there was any time when circumstances pointed towards the exit door, then the current scenario presents the best proposition.
Barcelona are at their weakest this season since Messi made his debut more than a decade back. An ageing squad and boardroom squabbles have badly affected the team and losing Neymar was a big body blow. Further, the famous La Masia production line has dried up due to a number of reasons as well.
Messi no longer has the regular service from the likes of Xavi, Andres Iniesta or Neymar anymore. The new contract he agreed to in the summer is yet to be signed and the Barcelona faithful will not breathe easy till the 30-year old extends his contract that expires in 2018. Even if he does, the release clause is rumoured to be €300 million.
While that figure definitely felt out of reach till July, Neymar's transfer has changed the landscape. Signing arguably the greatest player of this generation, if not of all time is a lure in itself. Now, taking into consideration that Messi has been a one-club man, any transfer that takes him away from Barcelona will create much more mind-boggling fracas than Neymar's transfer.
A recent reveal brought to light how Messi reportedly wanted to leave Barcelona last summer and move to former manager Pep Guardiola's Manchester City. While Messi considers his options given the state of his team and Madrid's domination in the final stages of this transfer window, there is no doubt that teams will not hesitate to move for him if the Argentine even drops a hint.
If that happens, then Messi will end this summer transfer window as the most expensive player ever.