4) Alexis Sanchez – Manchester United – £35m*
This deal has an asterisk beside it simply because United technically didn’t pay anything for the Chilean international in January 2018. However, they did send Henrikh Mkhitaryan to Arsenal as part of the deal and the Armenian was said to be worth £35m.
After a disastrous eighteen months with United, Sanchez moved on loan to Inter Milan before joining the Nerazzurri permanently on a free transfer in the summer of 2020.