4. Alex Oxlade-Chamberlain (€24.2m profit)
The first player on this list who was not involved in the Arsenal academy is Alex Oxlade-Chamberlain.
Originally signed by Arsenal from Southampton for €13.8m, Alex Oxlade-Chamberlain went onto become a great player under the mentorship of Arsene Wenger. The England international was trialed in a multitude of different positions including on the wing, in midfield and as a wing-back.
Being a first-team star who was plagued by injuries, it is easy to say that The Ox didn't live up to his true potential. However, Jurgen Klopp saw something in him and Liverpool eventually signed Alex Oxlade-Chamberlain for €38m in 2017. This secured a nice €24.2m profit for Arsenal, making Oxlade-Chamberlain.
Oxlade-Chamberlain went on to win the Premier League and the Champions League with Liverpool, so it's safe to say that he won't regret leaving Arsenal.
Continued on the next slide...