This is because when clubs sell academy graduates the entire transfer fee goes down as 'pure profit' in their financial accounts and can help them bypass the top flight's strict profit and sustainability rules.
One recent example was Conor Gallagher who was sold to Atletico Madrid this week despite being at the club since he was just 8 years old.
The 24-year-old joins a host of Chelsea talent that has been shown the door despite rising through the academy including: Mason Mount, Lewis Hall, Ruben Loftus-Cheek, Ian Maatsen, Callum Hudson-Odoi and Billy Gilmour.
Armando Broja and Trevoh Chalobah are also expected to join them in the coming months which does free up finances but it upsets fans and also Maresca who has spoken out about the issue.
"But this is not Chelsea's problem, these are the rules. All the clubs at this moment are compelled to sell players from the academy because of the rules. It's all of the Premier League clubs' problems.”
"It's not only us, it's all the Premier League clubs. It's a shame because in Italy, we have (Francesco) Totti with Roma, 20 years with the same club - one club man. We love that in football, the fans want to see that. But with the rules now it is different than the past.”
He was asked if Chelsea’s spending put the club in this position but did not back down.
"Yeah, but it is not only Chelsea spending money on players. It's all the big clubs to try and buy players.
"Some of the clubs spend more, some spend less. My personal opinion is it's a shame because we like to see a one club man but the rules are different."
When asked if the financial rules need changing, he was adamant.
"If they want to protect academy players, then probably yes."