Sometimes fans are shocked when they see their club sell their favourite players, like when Angel Di Maria was sold by Real Madrid. Click through our gallery to see 12 stars their old clubs might wish they never let go of.
Click through our gallery to see the stars at their former clubs.
When Chelsea sold Kevin De Bruyne to Wolfsburg in 2014, it seemed it was a case of the Belgian not being able to break into the Blues' first team, but today the midfielder is considered to be one of Europe's best attacking midfielders.
De Bruyne has since made an outstanding impact at Manchester City, scoring 16 goals and assisting a further 16 strikes in 39 matches this season.
Real Madrid have also made a few questionable decisions when it comes to selling their stars in the past, such as when Mesut Ozil was allowed to leave for Arsenal in 2013, while Di Maria followed a year later, joining Manchester United.
Chelsea could be kicking themselves for allowing Petr Cech to join London rivals Arsenal, while Inter Milan may be wishing they had never got rid of Philippe Coutinho three years ago.
Paul Pogba is a superstar many believe should have been held on to tightly by the Red Devils, while AC Milan might wish they sold Zlatan Ibrahimovic to Paris Saint-Germain for more than just £15 million (R307 million), considering the impact the Swede has had in France.
There are a few other stars certain clubs could regret selling, and you can view them in the gallery.
Can you name any other stars who could possibly fall into this bracket? Let us know in the comments section below.