The 18-year-old has completed a £35million switch to Premier League rivals Newcastle, with the Blues losing a left-back who impressed after breaking through last season.
Yet another fine product of Chelsea's Cobham academy, Hall departs after just 12 first team appearances, following his debut in January 2022.
Former manager Frank Lampard handed Hall his first senior minutes after an injury to first-choice Ben Chilwell, and insisted the 'really talented' full-back was set for a 'big future' at Stamford Bridge.
However, with competition in the shape of £60m Marc Cucurella and Ian Maatsen, Hall's fee represents pure profit in Chelsea's accounts during 18 months of staggering spending.
Nevertheless, Hall could join a long list of academy graduates who were turned into pure profit before having success elsewhere.
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That list includes Mason Mount, Marc Guehi, Fikayo Tomori, Tammy Abraham and Ruben Loftus-Cheek, and many fans fear Hall could be another that got away.
Some have even suggested the apparent strategy of using the academy for sales will be the club's downfall.
Twitter account Chelsea Youth responded to the news by telling their 260,000 followers: "Cobham will never be your get out of jail free card and the cold, transactional way you look upon the academy will prove to be your downfall."
They added: "If you haven't figured it out yet, Cobham will produce better players than you can recruit short, medium or long term, and no amount of finger-pointing or excuse-making will hide that fact. The evidence is there for you all to see. Transfers are made to satisfy ego.
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"To put your faith in recruiting better talent than your own academy can produce (with a proven track record) is either brave or stupid, or both. To put your faith in the people executing the plan without evidence of success first is naive."
A number of other fans expressed their disappointment with the news, with one writing: "[Todd] Boehly ripping the academy heart of the Chelsea squad in recent windows. For one reason only. Every academy player is pure profit and offsets his overspending."
Another added: "It's pretty simple, stop signing quite so many exciting youngsters and use the exciting youngsters you already have."
A third wrote: "We'll regret letting Lewis Hall go more then we regret letting Kevin De Bruyne and [Mohamed] Salah go."
While a final fan agreed, saying: "This one also hurts. Selling one of our brightest young talents to a top four competitor because we overpaid on a left-back option who is blocking his path... That's such a bad look. We're going to regret this. Lewis Hall already looks good enough to start at left-back."