The Blues have already allowed the likes of David Luiz, Ashley Cole, Frank Lampard, Samuel Eto'o and Demba Ba to leave the club this summer, with manager Jose Mourinho keen to have a partial overhaul of his squad having brought in Filipe Luis, Cesc Fabregas, Diego Costa and Didier Drogba.
Yet more departures could be around the corner, with Dutch left back van Aanholt set to switch Stamford Bridge for the Stadium of Light following interest from ex-Blues midfielder Gustavo Poyet. The Uruguayan has been pursuing a permanent deal for Fiorentina loanee Marcos Alonso for most of the summer, but having failed to agree terms with the Serie A side, he's switched his attention to van Aanholt.
Yet having impressed on loan with Vitesse Arnhem last season, should Chelsea have been looking to keep van Aanholt in West London rather than sell him?
Chelsea parted ways with long-serving Cole earlier this summer, with the 33-year-old moving to Italy for a new challenge with Roma. In his place came Atletico Madrid star Luis, and whilst the Brazilian is one of the best left backs in Europe, there are still question marks over the depth behind him.
Last season's starter Cesar Azpilicueta is more comfortable on the right hand side than the left, and whilst he filled in admirably last term, he's expected to start at right back this time around. Meanwhile, Ryan Bertrand is wanted by a host of clubs, including Liverpool - and if he goes, Chelsea are left a little short at left back.
Van Aanholt, 23, has spent the last three seasons on loan at Vitesse in his native Netherlands, and has impressed enough to land his first cap for his country. Whilst he didn't go to the World Cup, van Aanholt is still highly rated and is likely to play more of a part in the future.
With that in mind, keeping van Aanholt as a specialist left back deputy - rather than forcing Azpilicueta over there - would have been a smart move given the depth in other areas. If Bertrand also leaves, then plenty will be resting on Luis' shoulders, when they had an able deputy already at the club.
Yet now, he's a Sunderland player - and will no doubt be looking to prove Mourinho wrong this season and beyond.